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The transmitted power is stepped down in substations and fed to distribution transformers through primary feeders. Distribution transformers further step down the voltage for secondary distribution through distributors and service mains to consumer premises.

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The dimensions given in the standard are valid only for single-start threads. Use the below procedure to adjust the limits according to the number of starts.External threads (Screws) are not affected. The data for single-start threads should be used.For internal threads (Nuts), the allowance for major, minor, and pitch diameters is increased (relative to an equivalent single-start thread) by K x es. K depends on the number of starts: for 2 starts k=0.5, 3 starts k=0.75, and for 4 starts or more, k=1. Our Acme Thread Calculator also handles multiple-start threads!Length of EngagementIncreasing the length of the engagement means using a lengthier nut that can support higher forces. The data listed in ASTM B1.5 and the formulas given above are valid for engagement lengths up to twice the major diameter. The pitch diameter allowance (es) should be increased by 0.1 x es x (LE -  2 x d) when LE>2XD. Our Acme Thread Calculator also handles all engagement lengths.Related Glossary Terms:Lead (Threading)CNC MachineMajor DiameterTooth per inch (tpi)Thread Allowance (es)Minor DiameterPitch DiameterPitchThread Height (Depth)Tap Drill Size

ACME threaddimensions

Definition of terms:Allowance (Deviation): The minimum permissible distance between the basic and actual profile.Tolerance: The width of the tolerance field of a diameter on the actual thread profile. (Pitch, Major & Minor diameters)

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Series G & C have 3 preciosn classes:2G/2C – Least accurate and more commonly used.3G/3C – Medium accuracy.4G/4C – Highest accuracy, recommended to reduce backlash.Limits CalculationsASTM B1.5 defines how to calculate the tolerance of the following parameters:Major diameter (d / D)Minor diameter (d1 / D1)Pitch diameter (d2 / D2)Pitch & Lead (P / L)Angles between flanks (α)The below formulas are not valid for the following cases:Centralizes Acme series.Engagement lengths that are larger than twice the major diameter.Threads with multiple starts.TPI values that are not one of 2-6, 8, 10, 12, 14, or 16.Nominal diameters that are not one of 1/4, 5/16, 3/8, 7/16, 1/2, 3/4, 7/8, 1, 1-1/8, 1-1/4, 1-3/8, 1-1/2, 1-3/4, 2, 2-1/2, 2-3/4, 3, 3-1/2, 4, 4-1/2, or 5 Inches.For these cases, read the small print in ASTM B1.5 or use our Acme Thread Calculator  that handles all cases!Before calculating the limits, you need to obtain the following data:Allowance for major and minor diameters (el): Equals 0.002 for pitches of 10 TPI or coarser. For finer pitches, use 0.001.Allowance for pitch diameters (es): Should be obtained from ASM B1.5 (table 9). It cannot be calculated by a formula. You can either obtain it from the standard or use our below calculator.Payment options Pitch diameter tolerance (TD2): Should be obtained from ASM B1.5 (tables 5-7) or calculated with the below formula.\( TD_2 = K_P \times \sqrt{P} + K_D \times \sqrt{D} \)ClassKpKd2G / 3C0.030.0063G / 3C0.0140.00284G / 4C0.010.002Major diameter tolerance (Td): Equals to the TPI divided by 20. (But if less than 0.005, 0.005 should be used).After the above data has been obtained, you can proceed with the below formulas to calculate the limits. The below formulas are valid for all cases (Including The limitation listed above).Formulas for Limits of External Acme Thread\( \begin{array}{l} \large d_{max} = d_{nom} \\ \large d_{min} = d_{max}\,-\,T_d \\ \large d_{2\,max} = d_{2\,nom}\,-\,es \\ \large d_{2\,min} = d_{2\,max}\,-\,T_{d2} \\ \large d_{1\,max} = d_{1\,nom}\,-\,el \\ \large d_{1\,min} = d_{1\,max}\,-\,1.5 \times T_{d2} \end{array} \)Formulas for Limits of an Internal Acme Thread\( \begin{array}{l} \large D_{min} = D_{nom}\,+\,el \\ \large D_{max} = D_{min}\,+\,el \\ \large D_{2\,min} = D_{2\,nom} \\ \large D_{2\,max} = D_{2\,min}\,+\,T_{d2} \\ \large D_{1\,min} = D_{1\,nom} \\ \large D_{1\,max} = D_{1\,min}\,+\,T_{d} \end{array} \)Special ACME ThreadsBecause of the nature of its use cases and the limited list of standard configurations, special Acme threads are commonly used.What is considered a special Acme thread?A Diameter-Pitch combination that does not appear in this list.Multiple-Start threads.An engagement length that is larger than twice the major diameter.The Acme Thread Calculator  handles also Special Threads!Diameter-Pitch combinationsThe standard list of Acme threads in ASTM B1.5 has only one pitch option per diameter. However, “playing” with the pitch is an important design consideration since it allows us to increase the traverse speed by using a coarser pitch or increasing the accuracy by choosing a finer one. When opting for a special thread, ASTM B1.5 provides each pitch with the minimum and maximum allowed diameters.Premisable Diamter-Pitch CombinationsFor s thread with an intermediate pitch value, use the diameters shown for the next coarser pitch in the graph.To get the dimensions for such a thread, follow the formulas provided above or our Acme Thread Calculator, which knows how to handle any diameter-pitch combination.Multiple Start ThreadsMultiple-Start Acme threads are popular since they can bump up the traverse speed in multiples of 2, 3, 4, or more.The dimensions given in the standard are valid only for single-start threads. Use the below procedure to adjust the limits according to the number of starts.External threads (Screws) are not affected. The data for single-start threads should be used.For internal threads (Nuts), the allowance for major, minor, and pitch diameters is increased (relative to an equivalent single-start thread) by K x es. K depends on the number of starts: for 2 starts k=0.5, 3 starts k=0.75, and for 4 starts or more, k=1. Our Acme Thread Calculator also handles multiple-start threads!Length of EngagementIncreasing the length of the engagement means using a lengthier nut that can support higher forces. The data listed in ASTM B1.5 and the formulas given above are valid for engagement lengths up to twice the major diameter. The pitch diameter allowance (es) should be increased by 0.1 x es x (LE -  2 x d) when LE>2XD. Our Acme Thread Calculator also handles all engagement lengths.Related Glossary Terms:Lead (Threading)CNC MachineMajor DiameterTooth per inch (tpi)Thread Allowance (es)Minor DiameterPitch DiameterPitchThread Height (Depth)Tap Drill Size

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ACME – Table of ContentDesignationBasic DimensionsSymbolsFormulasDimensions ChartLimits of DimensionsSeries & ClassesLimits CalculationsSpecial ACME ThreadsDiameter-Pitch combinationsMultiple Start ThreadsLength of Engagement

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A reliable power distribution system is crucial for both residential and industrial power needs. Ring main distribution system is one such commonly used power distribution architecture.

ASTM B1.5 defines how to calculate the tolerance of the following parameters:Major diameter (d / D)Minor diameter (d1 / D1)Pitch diameter (d2 / D2)Pitch & Lead (P / L)Angles between flanks (α)The below formulas are not valid for the following cases:Centralizes Acme series.Engagement lengths that are larger than twice the major diameter.Threads with multiple starts.TPI values that are not one of 2-6, 8, 10, 12, 14, or 16.Nominal diameters that are not one of 1/4, 5/16, 3/8, 7/16, 1/2, 3/4, 7/8, 1, 1-1/8, 1-1/4, 1-3/8, 1-1/2, 1-3/4, 2, 2-1/2, 2-3/4, 3, 3-1/2, 4, 4-1/2, or 5 Inches.For these cases, read the small print in ASTM B1.5 or use our Acme Thread Calculator  that handles all cases!Before calculating the limits, you need to obtain the following data:Allowance for major and minor diameters (el): Equals 0.002 for pitches of 10 TPI or coarser. For finer pitches, use 0.001.Allowance for pitch diameters (es): Should be obtained from ASM B1.5 (table 9). It cannot be calculated by a formula. You can either obtain it from the standard or use our below calculator.Payment options Pitch diameter tolerance (TD2): Should be obtained from ASM B1.5 (tables 5-7) or calculated with the below formula.\( TD_2 = K_P \times \sqrt{P} + K_D \times \sqrt{D} \)ClassKpKd2G / 3C0.030.0063G / 3C0.0140.00284G / 4C0.010.002Major diameter tolerance (Td): Equals to the TPI divided by 20. (But if less than 0.005, 0.005 should be used).After the above data has been obtained, you can proceed with the below formulas to calculate the limits. The below formulas are valid for all cases (Including The limitation listed above).Formulas for Limits of External Acme Thread\( \begin{array}{l} \large d_{max} = d_{nom} \\ \large d_{min} = d_{max}\,-\,T_d \\ \large d_{2\,max} = d_{2\,nom}\,-\,es \\ \large d_{2\,min} = d_{2\,max}\,-\,T_{d2} \\ \large d_{1\,max} = d_{1\,nom}\,-\,el \\ \large d_{1\,min} = d_{1\,max}\,-\,1.5 \times T_{d2} \end{array} \)Formulas for Limits of an Internal Acme Thread\( \begin{array}{l} \large D_{min} = D_{nom}\,+\,el \\ \large D_{max} = D_{min}\,+\,el \\ \large D_{2\,min} = D_{2\,nom} \\ \large D_{2\,max} = D_{2\,min}\,+\,T_{d2} \\ \large D_{1\,min} = D_{1\,nom} \\ \large D_{1\,max} = D_{1\,min}\,+\,T_{d} \end{array} \)Special ACME ThreadsBecause of the nature of its use cases and the limited list of standard configurations, special Acme threads are commonly used.What is considered a special Acme thread?A Diameter-Pitch combination that does not appear in this list.Multiple-Start threads.An engagement length that is larger than twice the major diameter.The Acme Thread Calculator  handles also Special Threads!Diameter-Pitch combinationsThe standard list of Acme threads in ASTM B1.5 has only one pitch option per diameter. However, “playing” with the pitch is an important design consideration since it allows us to increase the traverse speed by using a coarser pitch or increasing the accuracy by choosing a finer one. When opting for a special thread, ASTM B1.5 provides each pitch with the minimum and maximum allowed diameters.Premisable Diamter-Pitch CombinationsFor s thread with an intermediate pitch value, use the diameters shown for the next coarser pitch in the graph.To get the dimensions for such a thread, follow the formulas provided above or our Acme Thread Calculator, which knows how to handle any diameter-pitch combination.Multiple Start ThreadsMultiple-Start Acme threads are popular since they can bump up the traverse speed in multiples of 2, 3, 4, or more.The dimensions given in the standard are valid only for single-start threads. Use the below procedure to adjust the limits according to the number of starts.External threads (Screws) are not affected. The data for single-start threads should be used.For internal threads (Nuts), the allowance for major, minor, and pitch diameters is increased (relative to an equivalent single-start thread) by K x es. K depends on the number of starts: for 2 starts k=0.5, 3 starts k=0.75, and for 4 starts or more, k=1. Our Acme Thread Calculator also handles multiple-start threads!Length of EngagementIncreasing the length of the engagement means using a lengthier nut that can support higher forces. The data listed in ASTM B1.5 and the formulas given above are valid for engagement lengths up to twice the major diameter. The pitch diameter allowance (es) should be increased by 0.1 x es x (LE -  2 x d) when LE>2XD. Our Acme Thread Calculator also handles all engagement lengths.Related Glossary Terms:Lead (Threading)CNC MachineMajor DiameterTooth per inch (tpi)Thread Allowance (es)Minor DiameterPitch DiameterPitchThread Height (Depth)Tap Drill Size

Because of the nature of its use cases and the limited list of standard configurations, special Acme threads are commonly used.What is considered a special Acme thread?A Diameter-Pitch combination that does not appear in this list.Multiple-Start threads.An engagement length that is larger than twice the major diameter.The Acme Thread Calculator  handles also Special Threads!Diameter-Pitch combinationsThe standard list of Acme threads in ASTM B1.5 has only one pitch option per diameter. However, “playing” with the pitch is an important design consideration since it allows us to increase the traverse speed by using a coarser pitch or increasing the accuracy by choosing a finer one. When opting for a special thread, ASTM B1.5 provides each pitch with the minimum and maximum allowed diameters.Premisable Diamter-Pitch CombinationsFor s thread with an intermediate pitch value, use the diameters shown for the next coarser pitch in the graph.To get the dimensions for such a thread, follow the formulas provided above or our Acme Thread Calculator, which knows how to handle any diameter-pitch combination.Multiple Start ThreadsMultiple-Start Acme threads are popular since they can bump up the traverse speed in multiples of 2, 3, 4, or more.The dimensions given in the standard are valid only for single-start threads. Use the below procedure to adjust the limits according to the number of starts.External threads (Screws) are not affected. The data for single-start threads should be used.For internal threads (Nuts), the allowance for major, minor, and pitch diameters is increased (relative to an equivalent single-start thread) by K x es. K depends on the number of starts: for 2 starts k=0.5, 3 starts k=0.75, and for 4 starts or more, k=1. Our Acme Thread Calculator also handles multiple-start threads!Length of EngagementIncreasing the length of the engagement means using a lengthier nut that can support higher forces. The data listed in ASTM B1.5 and the formulas given above are valid for engagement lengths up to twice the major diameter. The pitch diameter allowance (es) should be increased by 0.1 x es x (LE -  2 x d) when LE>2XD. Our Acme Thread Calculator also handles all engagement lengths.Related Glossary Terms:Lead (Threading)CNC MachineMajor DiameterTooth per inch (tpi)Thread Allowance (es)Minor DiameterPitch DiameterPitchThread Height (Depth)Tap Drill Size

Acme threadInsert

The ring main typically comprises Ring Circuit Breakers forming an outer ring, with Ring Feeders connected radially to it.

Its loop topology ensures redundancy and continuity of power supply even during feeder faults. Engineering drawings and diagrams help elucidate various power distribution techniques.

Distribution transformers and distributors are tapped off the ring feeders to supply consumer loads. Sectional Ring Main Units along the feeders allow the isolation of faulty sections.

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Class:The class is defined by a number between 2 and 4.2– Lower precision.4 – Higher precision.Internal and external designations are exactly the same. You cannot tell from the description alone if the thread is external or internal.Additional Parameters:Direction: By default, the thread is right-hand. For a left-hand thread, add the suffix -LH.Number of Starts: By default, all threads have a single start. Thus, the lead equals the pitch. For a multiple-start thread, the lead is also indicated by the letter L. For example, 1/4– 0.0625P – 0.1875L-ACMEdenotes a 0.25″ ACME thread with 3 starts. (0.1875/0.0625=3)Designation Examples of Acme ThreadsDesignationSeriesNominalDiameterTPIPitchLeadClassNumber of StartsThread Direction1/2-10-ACME 2GG0.5"100.1"=Pitch21Right Hand0.5-10-ACME 4CC0.5"100.1"=Pitch41Right Hand1/4– 0.0625P – 0.1875L-ACME 2GG0.25"160.0625"0.1875"23Right Hand2.5-3-ACME 4C-LHC2.5"30.3333"=Pitch41Left HandACME Threads – Basic DimensionsThe basic dimensions are nominal dimensions of the ACME profile without allowances and tolerances (The series and class define that – see below). They are based on standard ASTM B1.5. The basic dimensions can be used for design. However, for manufacturing and machining, you need the allowable range of each dimension. This data can be found in the ASTM standard or in the Limits and Dimensions section below. All the basic dimensions are derived from simple formulas based on the thread’s nominal diameter and pitch.SymbolsList of symbols used in charts and formulas of ACME ThreadsSymbolExplanationBasic Parameters - Diameters and PitchDMajor (Basic) diameter of internal threadD1Minor diameter of internal threadD2Pitch diameter of internal threaddExternal Major Diameterd1Minor diameter of external threadd2Pitch diameter of external threadnNumber of threds per Inch (TPI)PPitch (Distance)LLeadSNumber of StartshThread HeightFFlat WidthLELength of EngagmentαThread V half AngleAllowance, Deviation, and TolerancesTDTolerance - Minor diameter of internal thread & (Major Diameter)TD2Tolerance - Pitch diameter of internal threadTdTolerance - Minor diameter of external thread & (Major Diameter)Td2Tolerance - Minor diameter of external threadesAllowance - Pitch DiameterELAllowance - Major Diameter & (Minor Diameter)FormulasExternal Thread\( \begin{array}{l} \large d= \text{Diameter from designation} \\ \large n = \text{TPI from designation} \\ \large P = \frac{n}{TPI} \\ \large h = \frac{P}{2} \\ \large d _2= d\,-\,h \\ \large d_1 = d\,-\,P \\ \large F = 0.3707 \times P \\ \large 2\times\alpha = 29^{\circ} \\ \large \lambda = \tan^{-1} \left ( \frac{P \times S}{\pi \times d_2} \right ) \end{array} \)Internal thread\( \begin{array}{l} \large D= \text{Diameter from designation} \\ \large n = \text{TPI from designation} \\ \large P = \frac{n}{TPI} \\ \large h = \frac{P}{2} \\ \large D _2= D\,-\,h \\ \large D_1 = D\,-\,P \\ \large F = 0.3707 \times P \\ \large 2\times\alpha = 29^{\circ} \\ \large \lambda = \tan^{-1} \left ( \frac{P \times S}{\pi \times D_2} \right ) \end{array} \)Dimensions ChartClick the Thread Link to get the Full Thread Data for all classes in Inch and Metric units* Click icon to show Additional columns.(*) All dimensions are in InchesThreadMajor DiameterTPIPitchPitch DiameterMinor DiameterThread HeightFlat WidthLead AngleTap Drill Siuze1/4 - 16 ACME0.25160.06250.21880.18750.031250.02325.2°0.1875Metric Data ➢Tolerances ➢5/16 - 14 ACME0.3125140.07140.27680.24110.035710.02654.7°0.2411Metric Data ➢Tolerances ➢3/8 - 12 ACME0.375120.08330.33330.29170.041670.03094.55°0.2917Metric Data ➢Tolerances ➢7/16 - 12 ACME0.4375120.08330.39580.35420.041670.03093.83°0.3542Metric Data ➢Tolerances ➢1/2 - 10 ACME0.5100.10.450.40.050.03714.05°0.4Metric Data ➢Tolerances ➢5/8 - 8 ACME0.62580.1250.56250.50.06250.04634.05°0.5Metric Data ➢Tolerances ➢3/4 - 6 ACME0.7560.16670.66670.58330.083330.06184.55°0.5833Metric Data ➢Tolerances ➢7/8 - 6 ACME0.87560.16670.79170.70830.083330.06183.83°0.7083Metric Data ➢Tolerances ➢1 - 5 ACME150.20.90.80.10.07414.05°0.8Metric Data ➢Tolerances ➢1 1/8 - 5 ACME1.12550.21.0250.9250.10.07413.55°N/AMetric Data ➢Tolerances ➢1 1/4 - 5 ACME1.2550.21.151.050.10.07413.17°N/AMetric Data ➢Tolerances ➢1 3/8 - 4 ACME1.37540.251.251.1250.1250.09273.64°N/AMetric Data ➢Tolerances ➢1 1/2 - 4 ACME1.540.251.3751.250.1250.09273.31°N/AMetric Data ➢Tolerances ➢1 3/4 - 4 ACME1.7540.251.6251.50.1250.09272.8°N/AMetric Data ➢Tolerances ➢2 - 4 ACME240.251.8751.750.1250.09272.43°N/AMetric Data ➢Tolerances ➢2 1/4 - 3 ACME2.2530.33332.08331.91670.166670.12362.92°N/AMetric Data ➢Tolerances ➢2 1/2 - 3 ACME2.530.33332.33332.16670.166670.12362.6°N/AMetric Data ➢Tolerances ➢2 3/4 - 3 ACME2.7530.33332.58332.41670.166670.12362.35°N/AMetric Data ➢Tolerances ➢3 - 2 ACME320.52.752.50.250.18543.31°N/AMetric Data ➢Tolerances ➢3 1/2 - 2 ACME3.520.53.2530.250.18542.8°N/AMetric Data ➢Tolerances ➢4 - 2 ACME420.53.753.50.250.18542.43°N/AMetric Data ➢Tolerances ➢4 1/2 - 2 ACME4.520.54.2540.250.18542.14°N/AMetric Data ➢Tolerances ➢5 - 2 ACME520.54.754.50.250.18541.92°N/AMetric Data ➢Tolerances ➢ACME Threads – Limits of DimensionsTo manufacture or measure a thread, one has to know the maximum and minimum permissible values of the basic dimensions. These values are calculated according to the thread series and class (See below).Definition of terms:Allowance (Deviation): The minimum permissible distance between the basic and actual profile.Tolerance: The width of the tolerance field of a diameter on the actual thread profile. (Pitch, Major & Minor diameters)A small allowance means that the assembly of a male and female thread will be harder, but after assembly, there will be less freedom of movement.A large allowance means that the assembly of a male and female thread will be easier, but after assembly, there will be more freedom of movement.The allowance size does not influence a thread’s production difficulty or price.A wide tolerance is easier and cheaper to produce but yields a larger spread between threads.A narrow tolerance is challenging to produce and more expensive but yields a smaller spread between threads.Series & ClassesACME threads are divided into 3 series:G (General Purpose) – The most commonly used Acme threads. Wedging can occur under loads; therefore, it is recommended for applications where the screw and nut are supported individually.It has 3 precision classes 2G, 3G, and 4G.C (Centralized) – Tighter clearance between the internal and external threads. That prevents wedging on the flanks. More suitable for applications with higher load.It shares the exact basic dimensions of the C series. The difference is only in the tolerances.It has 3 precision classes 2C, 3C, and 4C.Stub – Compact threads with a 43% shorter stub height than standard Acme.Short and truncated thread profile, suitable for applications with limited space. Unlike G & C series, it only has a single precision class. They are defined in a separate ASTM document number B1.8.Series G & C have 3 preciosn classes:2G/2C – Least accurate and more commonly used.3G/3C – Medium accuracy.4G/4C – Highest accuracy, recommended to reduce backlash.Limits CalculationsASTM B1.5 defines how to calculate the tolerance of the following parameters:Major diameter (d / D)Minor diameter (d1 / D1)Pitch diameter (d2 / D2)Pitch & Lead (P / L)Angles between flanks (α)The below formulas are not valid for the following cases:Centralizes Acme series.Engagement lengths that are larger than twice the major diameter.Threads with multiple starts.TPI values that are not one of 2-6, 8, 10, 12, 14, or 16.Nominal diameters that are not one of 1/4, 5/16, 3/8, 7/16, 1/2, 3/4, 7/8, 1, 1-1/8, 1-1/4, 1-3/8, 1-1/2, 1-3/4, 2, 2-1/2, 2-3/4, 3, 3-1/2, 4, 4-1/2, or 5 Inches.For these cases, read the small print in ASTM B1.5 or use our Acme Thread Calculator  that handles all cases!Before calculating the limits, you need to obtain the following data:Allowance for major and minor diameters (el): Equals 0.002 for pitches of 10 TPI or coarser. For finer pitches, use 0.001.Allowance for pitch diameters (es): Should be obtained from ASM B1.5 (table 9). It cannot be calculated by a formula. You can either obtain it from the standard or use our below calculator.Payment options Pitch diameter tolerance (TD2): Should be obtained from ASM B1.5 (tables 5-7) or calculated with the below formula.\( TD_2 = K_P \times \sqrt{P} + K_D \times \sqrt{D} \)ClassKpKd2G / 3C0.030.0063G / 3C0.0140.00284G / 4C0.010.002Major diameter tolerance (Td): Equals to the TPI divided by 20. (But if less than 0.005, 0.005 should be used).After the above data has been obtained, you can proceed with the below formulas to calculate the limits. The below formulas are valid for all cases (Including The limitation listed above).Formulas for Limits of External Acme Thread\( \begin{array}{l} \large d_{max} = d_{nom} \\ \large d_{min} = d_{max}\,-\,T_d \\ \large d_{2\,max} = d_{2\,nom}\,-\,es \\ \large d_{2\,min} = d_{2\,max}\,-\,T_{d2} \\ \large d_{1\,max} = d_{1\,nom}\,-\,el \\ \large d_{1\,min} = d_{1\,max}\,-\,1.5 \times T_{d2} \end{array} \)Formulas for Limits of an Internal Acme Thread\( \begin{array}{l} \large D_{min} = D_{nom}\,+\,el \\ \large D_{max} = D_{min}\,+\,el \\ \large D_{2\,min} = D_{2\,nom} \\ \large D_{2\,max} = D_{2\,min}\,+\,T_{d2} \\ \large D_{1\,min} = D_{1\,nom} \\ \large D_{1\,max} = D_{1\,min}\,+\,T_{d} \end{array} \)Special ACME ThreadsBecause of the nature of its use cases and the limited list of standard configurations, special Acme threads are commonly used.What is considered a special Acme thread?A Diameter-Pitch combination that does not appear in this list.Multiple-Start threads.An engagement length that is larger than twice the major diameter.The Acme Thread Calculator  handles also Special Threads!Diameter-Pitch combinationsThe standard list of Acme threads in ASTM B1.5 has only one pitch option per diameter. However, “playing” with the pitch is an important design consideration since it allows us to increase the traverse speed by using a coarser pitch or increasing the accuracy by choosing a finer one. When opting for a special thread, ASTM B1.5 provides each pitch with the minimum and maximum allowed diameters.Premisable Diamter-Pitch CombinationsFor s thread with an intermediate pitch value, use the diameters shown for the next coarser pitch in the graph.To get the dimensions for such a thread, follow the formulas provided above or our Acme Thread Calculator, which knows how to handle any diameter-pitch combination.Multiple Start ThreadsMultiple-Start Acme threads are popular since they can bump up the traverse speed in multiples of 2, 3, 4, or more.The dimensions given in the standard are valid only for single-start threads. Use the below procedure to adjust the limits according to the number of starts.External threads (Screws) are not affected. The data for single-start threads should be used.For internal threads (Nuts), the allowance for major, minor, and pitch diameters is increased (relative to an equivalent single-start thread) by K x es. K depends on the number of starts: for 2 starts k=0.5, 3 starts k=0.75, and for 4 starts or more, k=1. Our Acme Thread Calculator also handles multiple-start threads!Length of EngagementIncreasing the length of the engagement means using a lengthier nut that can support higher forces. The data listed in ASTM B1.5 and the formulas given above are valid for engagement lengths up to twice the major diameter. The pitch diameter allowance (es) should be increased by 0.1 x es x (LE -  2 x d) when LE>2XD. Our Acme Thread Calculator also handles all engagement lengths.Related Glossary Terms:Lead (Threading)CNC MachineMajor DiameterTooth per inch (tpi)Thread Allowance (es)Minor DiameterPitch DiameterPitchThread Height (Depth)Tap Drill Size

ACME threadCalculator

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Distribution transformers step down the voltage and supply loads via distributors tapped from the ring. The ring main configuration allows each distributor to receive supply from two directions, providing redundancy in case of feeder faults.

Acme threadangle

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To manufacture or measure a thread, one has to know the maximum and minimum permissible values of the basic dimensions. These values are calculated according to the thread series and class (See below).Definition of terms:Allowance (Deviation): The minimum permissible distance between the basic and actual profile.Tolerance: The width of the tolerance field of a diameter on the actual thread profile. (Pitch, Major & Minor diameters)A small allowance means that the assembly of a male and female thread will be harder, but after assembly, there will be less freedom of movement.A large allowance means that the assembly of a male and female thread will be easier, but after assembly, there will be more freedom of movement.The allowance size does not influence a thread’s production difficulty or price.A wide tolerance is easier and cheaper to produce but yields a larger spread between threads.A narrow tolerance is challenging to produce and more expensive but yields a smaller spread between threads.Series & ClassesACME threads are divided into 3 series:G (General Purpose) – The most commonly used Acme threads. Wedging can occur under loads; therefore, it is recommended for applications where the screw and nut are supported individually.It has 3 precision classes 2G, 3G, and 4G.C (Centralized) – Tighter clearance between the internal and external threads. That prevents wedging on the flanks. More suitable for applications with higher load.It shares the exact basic dimensions of the C series. The difference is only in the tolerances.It has 3 precision classes 2C, 3C, and 4C.Stub – Compact threads with a 43% shorter stub height than standard Acme.Short and truncated thread profile, suitable for applications with limited space. Unlike G & C series, it only has a single precision class. They are defined in a separate ASTM document number B1.8.Series G & C have 3 preciosn classes:2G/2C – Least accurate and more commonly used.3G/3C – Medium accuracy.4G/4C – Highest accuracy, recommended to reduce backlash.Limits CalculationsASTM B1.5 defines how to calculate the tolerance of the following parameters:Major diameter (d / D)Minor diameter (d1 / D1)Pitch diameter (d2 / D2)Pitch & Lead (P / L)Angles between flanks (α)The below formulas are not valid for the following cases:Centralizes Acme series.Engagement lengths that are larger than twice the major diameter.Threads with multiple starts.TPI values that are not one of 2-6, 8, 10, 12, 14, or 16.Nominal diameters that are not one of 1/4, 5/16, 3/8, 7/16, 1/2, 3/4, 7/8, 1, 1-1/8, 1-1/4, 1-3/8, 1-1/2, 1-3/4, 2, 2-1/2, 2-3/4, 3, 3-1/2, 4, 4-1/2, or 5 Inches.For these cases, read the small print in ASTM B1.5 or use our Acme Thread Calculator  that handles all cases!Before calculating the limits, you need to obtain the following data:Allowance for major and minor diameters (el): Equals 0.002 for pitches of 10 TPI or coarser. For finer pitches, use 0.001.Allowance for pitch diameters (es): Should be obtained from ASM B1.5 (table 9). It cannot be calculated by a formula. You can either obtain it from the standard or use our below calculator.Payment options Pitch diameter tolerance (TD2): Should be obtained from ASM B1.5 (tables 5-7) or calculated with the below formula.\( TD_2 = K_P \times \sqrt{P} + K_D \times \sqrt{D} \)ClassKpKd2G / 3C0.030.0063G / 3C0.0140.00284G / 4C0.010.002Major diameter tolerance (Td): Equals to the TPI divided by 20. (But if less than 0.005, 0.005 should be used).After the above data has been obtained, you can proceed with the below formulas to calculate the limits. The below formulas are valid for all cases (Including The limitation listed above).Formulas for Limits of External Acme Thread\( \begin{array}{l} \large d_{max} = d_{nom} \\ \large d_{min} = d_{max}\,-\,T_d \\ \large d_{2\,max} = d_{2\,nom}\,-\,es \\ \large d_{2\,min} = d_{2\,max}\,-\,T_{d2} \\ \large d_{1\,max} = d_{1\,nom}\,-\,el \\ \large d_{1\,min} = d_{1\,max}\,-\,1.5 \times T_{d2} \end{array} \)Formulas for Limits of an Internal Acme Thread\( \begin{array}{l} \large D_{min} = D_{nom}\,+\,el \\ \large D_{max} = D_{min}\,+\,el \\ \large D_{2\,min} = D_{2\,nom} \\ \large D_{2\,max} = D_{2\,min}\,+\,T_{d2} \\ \large D_{1\,min} = D_{1\,nom} \\ \large D_{1\,max} = D_{1\,min}\,+\,T_{d} \end{array} \)Special ACME ThreadsBecause of the nature of its use cases and the limited list of standard configurations, special Acme threads are commonly used.What is considered a special Acme thread?A Diameter-Pitch combination that does not appear in this list.Multiple-Start threads.An engagement length that is larger than twice the major diameter.The Acme Thread Calculator  handles also Special Threads!Diameter-Pitch combinationsThe standard list of Acme threads in ASTM B1.5 has only one pitch option per diameter. However, “playing” with the pitch is an important design consideration since it allows us to increase the traverse speed by using a coarser pitch or increasing the accuracy by choosing a finer one. When opting for a special thread, ASTM B1.5 provides each pitch with the minimum and maximum allowed diameters.Premisable Diamter-Pitch CombinationsFor s thread with an intermediate pitch value, use the diameters shown for the next coarser pitch in the graph.To get the dimensions for such a thread, follow the formulas provided above or our Acme Thread Calculator, which knows how to handle any diameter-pitch combination.Multiple Start ThreadsMultiple-Start Acme threads are popular since they can bump up the traverse speed in multiples of 2, 3, 4, or more.The dimensions given in the standard are valid only for single-start threads. Use the below procedure to adjust the limits according to the number of starts.External threads (Screws) are not affected. The data for single-start threads should be used.For internal threads (Nuts), the allowance for major, minor, and pitch diameters is increased (relative to an equivalent single-start thread) by K x es. K depends on the number of starts: for 2 starts k=0.5, 3 starts k=0.75, and for 4 starts or more, k=1. Our Acme Thread Calculator also handles multiple-start threads!Length of EngagementIncreasing the length of the engagement means using a lengthier nut that can support higher forces. The data listed in ASTM B1.5 and the formulas given above are valid for engagement lengths up to twice the major diameter. The pitch diameter allowance (es) should be increased by 0.1 x es x (LE -  2 x d) when LE>2XD. Our Acme Thread Calculator also handles all engagement lengths.Related Glossary Terms:Lead (Threading)CNC MachineMajor DiameterTooth per inch (tpi)Thread Allowance (es)Minor DiameterPitch DiameterPitchThread Height (Depth)Tap Drill Size

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What is considered a special Acme thread?A Diameter-Pitch combination that does not appear in this list.Multiple-Start threads.An engagement length that is larger than twice the major diameter.The Acme Thread Calculator  handles also Special Threads!Diameter-Pitch combinationsThe standard list of Acme threads in ASTM B1.5 has only one pitch option per diameter. However, “playing” with the pitch is an important design consideration since it allows us to increase the traverse speed by using a coarser pitch or increasing the accuracy by choosing a finer one. When opting for a special thread, ASTM B1.5 provides each pitch with the minimum and maximum allowed diameters.Premisable Diamter-Pitch CombinationsFor s thread with an intermediate pitch value, use the diameters shown for the next coarser pitch in the graph.To get the dimensions for such a thread, follow the formulas provided above or our Acme Thread Calculator, which knows how to handle any diameter-pitch combination.Multiple Start ThreadsMultiple-Start Acme threads are popular since they can bump up the traverse speed in multiples of 2, 3, 4, or more.The dimensions given in the standard are valid only for single-start threads. Use the below procedure to adjust the limits according to the number of starts.External threads (Screws) are not affected. The data for single-start threads should be used.For internal threads (Nuts), the allowance for major, minor, and pitch diameters is increased (relative to an equivalent single-start thread) by K x es. K depends on the number of starts: for 2 starts k=0.5, 3 starts k=0.75, and for 4 starts or more, k=1. Our Acme Thread Calculator also handles multiple-start threads!Length of EngagementIncreasing the length of the engagement means using a lengthier nut that can support higher forces. The data listed in ASTM B1.5 and the formulas given above are valid for engagement lengths up to twice the major diameter. The pitch diameter allowance (es) should be increased by 0.1 x es x (LE -  2 x d) when LE>2XD. Our Acme Thread Calculator also handles all engagement lengths.Related Glossary Terms:Lead (Threading)CNC MachineMajor DiameterTooth per inch (tpi)Thread Allowance (es)Minor DiameterPitch DiameterPitchThread Height (Depth)Tap Drill Size

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The standard list of Acme threads in ASTM B1.5 has only one pitch option per diameter. However, “playing” with the pitch is an important design consideration since it allows us to increase the traverse speed by using a coarser pitch or increasing the accuracy by choosing a finer one. When opting for a special thread, ASTM B1.5 provides each pitch with the minimum and maximum allowed diameters.Premisable Diamter-Pitch CombinationsFor s thread with an intermediate pitch value, use the diameters shown for the next coarser pitch in the graph.To get the dimensions for such a thread, follow the formulas provided above or our Acme Thread Calculator, which knows how to handle any diameter-pitch combination.Multiple Start ThreadsMultiple-Start Acme threads are popular since they can bump up the traverse speed in multiples of 2, 3, 4, or more.The dimensions given in the standard are valid only for single-start threads. Use the below procedure to adjust the limits according to the number of starts.External threads (Screws) are not affected. The data for single-start threads should be used.For internal threads (Nuts), the allowance for major, minor, and pitch diameters is increased (relative to an equivalent single-start thread) by K x es. K depends on the number of starts: for 2 starts k=0.5, 3 starts k=0.75, and for 4 starts or more, k=1. Our Acme Thread Calculator also handles multiple-start threads!Length of EngagementIncreasing the length of the engagement means using a lengthier nut that can support higher forces. The data listed in ASTM B1.5 and the formulas given above are valid for engagement lengths up to twice the major diameter. The pitch diameter allowance (es) should be increased by 0.1 x es x (LE -  2 x d) when LE>2XD. Our Acme Thread Calculator also handles all engagement lengths.Related Glossary Terms:Lead (Threading)CNC MachineMajor DiameterTooth per inch (tpi)Thread Allowance (es)Minor DiameterPitch DiameterPitchThread Height (Depth)Tap Drill Size

The Acme Thread Calculator  handles also Special Threads!Diameter-Pitch combinationsThe standard list of Acme threads in ASTM B1.5 has only one pitch option per diameter. However, “playing” with the pitch is an important design consideration since it allows us to increase the traverse speed by using a coarser pitch or increasing the accuracy by choosing a finer one. When opting for a special thread, ASTM B1.5 provides each pitch with the minimum and maximum allowed diameters.Premisable Diamter-Pitch CombinationsFor s thread with an intermediate pitch value, use the diameters shown for the next coarser pitch in the graph.To get the dimensions for such a thread, follow the formulas provided above or our Acme Thread Calculator, which knows how to handle any diameter-pitch combination.Multiple Start ThreadsMultiple-Start Acme threads are popular since they can bump up the traverse speed in multiples of 2, 3, 4, or more.The dimensions given in the standard are valid only for single-start threads. Use the below procedure to adjust the limits according to the number of starts.External threads (Screws) are not affected. The data for single-start threads should be used.For internal threads (Nuts), the allowance for major, minor, and pitch diameters is increased (relative to an equivalent single-start thread) by K x es. K depends on the number of starts: for 2 starts k=0.5, 3 starts k=0.75, and for 4 starts or more, k=1. Our Acme Thread Calculator also handles multiple-start threads!Length of EngagementIncreasing the length of the engagement means using a lengthier nut that can support higher forces. The data listed in ASTM B1.5 and the formulas given above are valid for engagement lengths up to twice the major diameter. The pitch diameter allowance (es) should be increased by 0.1 x es x (LE -  2 x d) when LE>2XD. Our Acme Thread Calculator also handles all engagement lengths.Related Glossary Terms:Lead (Threading)CNC MachineMajor DiameterTooth per inch (tpi)Thread Allowance (es)Minor DiameterPitch DiameterPitchThread Height (Depth)Tap Drill Size

Additional Parameters:Direction: By default, the thread is right-hand. For a left-hand thread, add the suffix -LH.Number of Starts: By default, all threads have a single start. Thus, the lead equals the pitch. For a multiple-start thread, the lead is also indicated by the letter L. For example, 1/4– 0.0625P – 0.1875L-ACMEdenotes a 0.25″ ACME thread with 3 starts. (0.1875/0.0625=3)Designation Examples of Acme ThreadsDesignationSeriesNominalDiameterTPIPitchLeadClassNumber of StartsThread Direction1/2-10-ACME 2GG0.5"100.1"=Pitch21Right Hand0.5-10-ACME 4CC0.5"100.1"=Pitch41Right Hand1/4– 0.0625P – 0.1875L-ACME 2GG0.25"160.0625"0.1875"23Right Hand2.5-3-ACME 4C-LHC2.5"30.3333"=Pitch41Left HandACME Threads – Basic DimensionsThe basic dimensions are nominal dimensions of the ACME profile without allowances and tolerances (The series and class define that – see below). They are based on standard ASTM B1.5. The basic dimensions can be used for design. However, for manufacturing and machining, you need the allowable range of each dimension. This data can be found in the ASTM standard or in the Limits and Dimensions section below. All the basic dimensions are derived from simple formulas based on the thread’s nominal diameter and pitch.SymbolsList of symbols used in charts and formulas of ACME ThreadsSymbolExplanationBasic Parameters - Diameters and PitchDMajor (Basic) diameter of internal threadD1Minor diameter of internal threadD2Pitch diameter of internal threaddExternal Major Diameterd1Minor diameter of external threadd2Pitch diameter of external threadnNumber of threds per Inch (TPI)PPitch (Distance)LLeadSNumber of StartshThread HeightFFlat WidthLELength of EngagmentαThread V half AngleAllowance, Deviation, and TolerancesTDTolerance - Minor diameter of internal thread & (Major Diameter)TD2Tolerance - Pitch diameter of internal threadTdTolerance - Minor diameter of external thread & (Major Diameter)Td2Tolerance - Minor diameter of external threadesAllowance - Pitch DiameterELAllowance - Major Diameter & (Minor Diameter)FormulasExternal Thread\( \begin{array}{l} \large d= \text{Diameter from designation} \\ \large n = \text{TPI from designation} \\ \large P = \frac{n}{TPI} \\ \large h = \frac{P}{2} \\ \large d _2= d\,-\,h \\ \large d_1 = d\,-\,P \\ \large F = 0.3707 \times P \\ \large 2\times\alpha = 29^{\circ} \\ \large \lambda = \tan^{-1} \left ( \frac{P \times S}{\pi \times d_2} \right ) \end{array} \)Internal thread\( \begin{array}{l} \large D= \text{Diameter from designation} \\ \large n = \text{TPI from designation} \\ \large P = \frac{n}{TPI} \\ \large h = \frac{P}{2} \\ \large D _2= D\,-\,h \\ \large D_1 = D\,-\,P \\ \large F = 0.3707 \times P \\ \large 2\times\alpha = 29^{\circ} \\ \large \lambda = \tan^{-1} \left ( \frac{P \times S}{\pi \times D_2} \right ) \end{array} \)Dimensions ChartClick the Thread Link to get the Full Thread Data for all classes in Inch and Metric units* Click icon to show Additional columns.(*) All dimensions are in InchesThreadMajor DiameterTPIPitchPitch DiameterMinor DiameterThread HeightFlat WidthLead AngleTap Drill Siuze1/4 - 16 ACME0.25160.06250.21880.18750.031250.02325.2°0.1875Metric Data ➢Tolerances ➢5/16 - 14 ACME0.3125140.07140.27680.24110.035710.02654.7°0.2411Metric Data ➢Tolerances ➢3/8 - 12 ACME0.375120.08330.33330.29170.041670.03094.55°0.2917Metric Data ➢Tolerances ➢7/16 - 12 ACME0.4375120.08330.39580.35420.041670.03093.83°0.3542Metric Data ➢Tolerances ➢1/2 - 10 ACME0.5100.10.450.40.050.03714.05°0.4Metric Data ➢Tolerances ➢5/8 - 8 ACME0.62580.1250.56250.50.06250.04634.05°0.5Metric Data ➢Tolerances ➢3/4 - 6 ACME0.7560.16670.66670.58330.083330.06184.55°0.5833Metric Data ➢Tolerances ➢7/8 - 6 ACME0.87560.16670.79170.70830.083330.06183.83°0.7083Metric Data ➢Tolerances ➢1 - 5 ACME150.20.90.80.10.07414.05°0.8Metric Data ➢Tolerances ➢1 1/8 - 5 ACME1.12550.21.0250.9250.10.07413.55°N/AMetric Data ➢Tolerances ➢1 1/4 - 5 ACME1.2550.21.151.050.10.07413.17°N/AMetric Data ➢Tolerances ➢1 3/8 - 4 ACME1.37540.251.251.1250.1250.09273.64°N/AMetric Data ➢Tolerances ➢1 1/2 - 4 ACME1.540.251.3751.250.1250.09273.31°N/AMetric Data ➢Tolerances ➢1 3/4 - 4 ACME1.7540.251.6251.50.1250.09272.8°N/AMetric Data ➢Tolerances ➢2 - 4 ACME240.251.8751.750.1250.09272.43°N/AMetric Data ➢Tolerances ➢2 1/4 - 3 ACME2.2530.33332.08331.91670.166670.12362.92°N/AMetric Data ➢Tolerances ➢2 1/2 - 3 ACME2.530.33332.33332.16670.166670.12362.6°N/AMetric Data ➢Tolerances ➢2 3/4 - 3 ACME2.7530.33332.58332.41670.166670.12362.35°N/AMetric Data ➢Tolerances ➢3 - 2 ACME320.52.752.50.250.18543.31°N/AMetric Data ➢Tolerances ➢3 1/2 - 2 ACME3.520.53.2530.250.18542.8°N/AMetric Data ➢Tolerances ➢4 - 2 ACME420.53.753.50.250.18542.43°N/AMetric Data ➢Tolerances ➢4 1/2 - 2 ACME4.520.54.2540.250.18542.14°N/AMetric Data ➢Tolerances ➢5 - 2 ACME520.54.754.50.250.18541.92°N/AMetric Data ➢Tolerances ➢ACME Threads – Limits of DimensionsTo manufacture or measure a thread, one has to know the maximum and minimum permissible values of the basic dimensions. These values are calculated according to the thread series and class (See below).Definition of terms:Allowance (Deviation): The minimum permissible distance between the basic and actual profile.Tolerance: The width of the tolerance field of a diameter on the actual thread profile. (Pitch, Major & Minor diameters)A small allowance means that the assembly of a male and female thread will be harder, but after assembly, there will be less freedom of movement.A large allowance means that the assembly of a male and female thread will be easier, but after assembly, there will be more freedom of movement.The allowance size does not influence a thread’s production difficulty or price.A wide tolerance is easier and cheaper to produce but yields a larger spread between threads.A narrow tolerance is challenging to produce and more expensive but yields a smaller spread between threads.Series & ClassesACME threads are divided into 3 series:G (General Purpose) – The most commonly used Acme threads. Wedging can occur under loads; therefore, it is recommended for applications where the screw and nut are supported individually.It has 3 precision classes 2G, 3G, and 4G.C (Centralized) – Tighter clearance between the internal and external threads. That prevents wedging on the flanks. More suitable for applications with higher load.It shares the exact basic dimensions of the C series. The difference is only in the tolerances.It has 3 precision classes 2C, 3C, and 4C.Stub – Compact threads with a 43% shorter stub height than standard Acme.Short and truncated thread profile, suitable for applications with limited space. Unlike G & C series, it only has a single precision class. They are defined in a separate ASTM document number B1.8.Series G & C have 3 preciosn classes:2G/2C – Least accurate and more commonly used.3G/3C – Medium accuracy.4G/4C – Highest accuracy, recommended to reduce backlash.Limits CalculationsASTM B1.5 defines how to calculate the tolerance of the following parameters:Major diameter (d / D)Minor diameter (d1 / D1)Pitch diameter (d2 / D2)Pitch & Lead (P / L)Angles between flanks (α)The below formulas are not valid for the following cases:Centralizes Acme series.Engagement lengths that are larger than twice the major diameter.Threads with multiple starts.TPI values that are not one of 2-6, 8, 10, 12, 14, or 16.Nominal diameters that are not one of 1/4, 5/16, 3/8, 7/16, 1/2, 3/4, 7/8, 1, 1-1/8, 1-1/4, 1-3/8, 1-1/2, 1-3/4, 2, 2-1/2, 2-3/4, 3, 3-1/2, 4, 4-1/2, or 5 Inches.For these cases, read the small print in ASTM B1.5 or use our Acme Thread Calculator  that handles all cases!Before calculating the limits, you need to obtain the following data:Allowance for major and minor diameters (el): Equals 0.002 for pitches of 10 TPI or coarser. For finer pitches, use 0.001.Allowance for pitch diameters (es): Should be obtained from ASM B1.5 (table 9). It cannot be calculated by a formula. You can either obtain it from the standard or use our below calculator.Payment options Pitch diameter tolerance (TD2): Should be obtained from ASM B1.5 (tables 5-7) or calculated with the below formula.\( TD_2 = K_P \times \sqrt{P} + K_D \times \sqrt{D} \)ClassKpKd2G / 3C0.030.0063G / 3C0.0140.00284G / 4C0.010.002Major diameter tolerance (Td): Equals to the TPI divided by 20. (But if less than 0.005, 0.005 should be used).After the above data has been obtained, you can proceed with the below formulas to calculate the limits. The below formulas are valid for all cases (Including The limitation listed above).Formulas for Limits of External Acme Thread\( \begin{array}{l} \large d_{max} = d_{nom} \\ \large d_{min} = d_{max}\,-\,T_d \\ \large d_{2\,max} = d_{2\,nom}\,-\,es \\ \large d_{2\,min} = d_{2\,max}\,-\,T_{d2} \\ \large d_{1\,max} = d_{1\,nom}\,-\,el \\ \large d_{1\,min} = d_{1\,max}\,-\,1.5 \times T_{d2} \end{array} \)Formulas for Limits of an Internal Acme Thread\( \begin{array}{l} \large D_{min} = D_{nom}\,+\,el \\ \large D_{max} = D_{min}\,+\,el \\ \large D_{2\,min} = D_{2\,nom} \\ \large D_{2\,max} = D_{2\,min}\,+\,T_{d2} \\ \large D_{1\,min} = D_{1\,nom} \\ \large D_{1\,max} = D_{1\,min}\,+\,T_{d} \end{array} \)Special ACME ThreadsBecause of the nature of its use cases and the limited list of standard configurations, special Acme threads are commonly used.What is considered a special Acme thread?A Diameter-Pitch combination that does not appear in this list.Multiple-Start threads.An engagement length that is larger than twice the major diameter.The Acme Thread Calculator  handles also Special Threads!Diameter-Pitch combinationsThe standard list of Acme threads in ASTM B1.5 has only one pitch option per diameter. However, “playing” with the pitch is an important design consideration since it allows us to increase the traverse speed by using a coarser pitch or increasing the accuracy by choosing a finer one. When opting for a special thread, ASTM B1.5 provides each pitch with the minimum and maximum allowed diameters.Premisable Diamter-Pitch CombinationsFor s thread with an intermediate pitch value, use the diameters shown for the next coarser pitch in the graph.To get the dimensions for such a thread, follow the formulas provided above or our Acme Thread Calculator, which knows how to handle any diameter-pitch combination.Multiple Start ThreadsMultiple-Start Acme threads are popular since they can bump up the traverse speed in multiples of 2, 3, 4, or more.The dimensions given in the standard are valid only for single-start threads. Use the below procedure to adjust the limits according to the number of starts.External threads (Screws) are not affected. The data for single-start threads should be used.For internal threads (Nuts), the allowance for major, minor, and pitch diameters is increased (relative to an equivalent single-start thread) by K x es. K depends on the number of starts: for 2 starts k=0.5, 3 starts k=0.75, and for 4 starts or more, k=1. Our Acme Thread Calculator also handles multiple-start threads!Length of EngagementIncreasing the length of the engagement means using a lengthier nut that can support higher forces. The data listed in ASTM B1.5 and the formulas given above are valid for engagement lengths up to twice the major diameter. The pitch diameter allowance (es) should be increased by 0.1 x es x (LE -  2 x d) when LE>2XD. Our Acme Thread Calculator also handles all engagement lengths.Related Glossary Terms:Lead (Threading)CNC MachineMajor DiameterTooth per inch (tpi)Thread Allowance (es)Minor DiameterPitch DiameterPitchThread Height (Depth)Tap Drill Size

For these cases, read the small print in ASTM B1.5 or use our Acme Thread Calculator  that handles all cases!Before calculating the limits, you need to obtain the following data:Allowance for major and minor diameters (el): Equals 0.002 for pitches of 10 TPI or coarser. For finer pitches, use 0.001.Allowance for pitch diameters (es): Should be obtained from ASM B1.5 (table 9). It cannot be calculated by a formula. You can either obtain it from the standard or use our below calculator.Payment options Pitch diameter tolerance (TD2): Should be obtained from ASM B1.5 (tables 5-7) or calculated with the below formula.\( TD_2 = K_P \times \sqrt{P} + K_D \times \sqrt{D} \)ClassKpKd2G / 3C0.030.0063G / 3C0.0140.00284G / 4C0.010.002Major diameter tolerance (Td): Equals to the TPI divided by 20. (But if less than 0.005, 0.005 should be used).After the above data has been obtained, you can proceed with the below formulas to calculate the limits. The below formulas are valid for all cases (Including The limitation listed above).Formulas for Limits of External Acme Thread\( \begin{array}{l} \large d_{max} = d_{nom} \\ \large d_{min} = d_{max}\,-\,T_d \\ \large d_{2\,max} = d_{2\,nom}\,-\,es \\ \large d_{2\,min} = d_{2\,max}\,-\,T_{d2} \\ \large d_{1\,max} = d_{1\,nom}\,-\,el \\ \large d_{1\,min} = d_{1\,max}\,-\,1.5 \times T_{d2} \end{array} \)Formulas for Limits of an Internal Acme Thread\( \begin{array}{l} \large D_{min} = D_{nom}\,+\,el \\ \large D_{max} = D_{min}\,+\,el \\ \large D_{2\,min} = D_{2\,nom} \\ \large D_{2\,max} = D_{2\,min}\,+\,T_{d2} \\ \large D_{1\,min} = D_{1\,nom} \\ \large D_{1\,max} = D_{1\,min}\,+\,T_{d} \end{array} \)Special ACME ThreadsBecause of the nature of its use cases and the limited list of standard configurations, special Acme threads are commonly used.What is considered a special Acme thread?A Diameter-Pitch combination that does not appear in this list.Multiple-Start threads.An engagement length that is larger than twice the major diameter.The Acme Thread Calculator  handles also Special Threads!Diameter-Pitch combinationsThe standard list of Acme threads in ASTM B1.5 has only one pitch option per diameter. However, “playing” with the pitch is an important design consideration since it allows us to increase the traverse speed by using a coarser pitch or increasing the accuracy by choosing a finer one. When opting for a special thread, ASTM B1.5 provides each pitch with the minimum and maximum allowed diameters.Premisable Diamter-Pitch CombinationsFor s thread with an intermediate pitch value, use the diameters shown for the next coarser pitch in the graph.To get the dimensions for such a thread, follow the formulas provided above or our Acme Thread Calculator, which knows how to handle any diameter-pitch combination.Multiple Start ThreadsMultiple-Start Acme threads are popular since they can bump up the traverse speed in multiples of 2, 3, 4, or more.The dimensions given in the standard are valid only for single-start threads. Use the below procedure to adjust the limits according to the number of starts.External threads (Screws) are not affected. The data for single-start threads should be used.For internal threads (Nuts), the allowance for major, minor, and pitch diameters is increased (relative to an equivalent single-start thread) by K x es. K depends on the number of starts: for 2 starts k=0.5, 3 starts k=0.75, and for 4 starts or more, k=1. Our Acme Thread Calculator also handles multiple-start threads!Length of EngagementIncreasing the length of the engagement means using a lengthier nut that can support higher forces. The data listed in ASTM B1.5 and the formulas given above are valid for engagement lengths up to twice the major diameter. The pitch diameter allowance (es) should be increased by 0.1 x es x (LE -  2 x d) when LE>2XD. Our Acme Thread Calculator also handles all engagement lengths.Related Glossary Terms:Lead (Threading)CNC MachineMajor DiameterTooth per inch (tpi)Thread Allowance (es)Minor DiameterPitch DiameterPitchThread Height (Depth)Tap Drill Size

Easly obtain all the dimensions and tolerances with our Acme Thread Calculator DesignationBasic designation syntax:Nominal Diameter in Inch FractionPitch in TPISeries: G – General / C – CentralizedClass: 2, 3, or 4. Indicates the precision.Diameter:The diameter can range between 1/4″ to 5″.It is also allowed to denote the diameters with a decimal value. For example, 0.250 (1/4″), 0.4375 (7/16″), etc.Pitch:By default, the pitch is given in TPI. For example, 1/4-20 means a thread with a pitch of 20 TPI (1/20=0.05″).On multiple starts threads (see below), the pitch is indicated by distance. For example, 1/4-0.05P means a thread with a pitch of 0.05″ (same as 20 TPI).Series:G – General use.C – Centralized. This class defines a more restricted clearance at the major diameter of both the internal and external screws that prevent wedging on the flanks.Class:The class is defined by a number between 2 and 4.2– Lower precision.4 – Higher precision.Internal and external designations are exactly the same. You cannot tell from the description alone if the thread is external or internal.Additional Parameters:Direction: By default, the thread is right-hand. For a left-hand thread, add the suffix -LH.Number of Starts: By default, all threads have a single start. Thus, the lead equals the pitch. For a multiple-start thread, the lead is also indicated by the letter L. For example, 1/4– 0.0625P – 0.1875L-ACMEdenotes a 0.25″ ACME thread with 3 starts. (0.1875/0.0625=3)Designation Examples of Acme ThreadsDesignationSeriesNominalDiameterTPIPitchLeadClassNumber of StartsThread Direction1/2-10-ACME 2GG0.5"100.1"=Pitch21Right Hand0.5-10-ACME 4CC0.5"100.1"=Pitch41Right Hand1/4– 0.0625P – 0.1875L-ACME 2GG0.25"160.0625"0.1875"23Right Hand2.5-3-ACME 4C-LHC2.5"30.3333"=Pitch41Left HandACME Threads – Basic DimensionsThe basic dimensions are nominal dimensions of the ACME profile without allowances and tolerances (The series and class define that – see below). They are based on standard ASTM B1.5. The basic dimensions can be used for design. However, for manufacturing and machining, you need the allowable range of each dimension. This data can be found in the ASTM standard or in the Limits and Dimensions section below. All the basic dimensions are derived from simple formulas based on the thread’s nominal diameter and pitch.SymbolsList of symbols used in charts and formulas of ACME ThreadsSymbolExplanationBasic Parameters - Diameters and PitchDMajor (Basic) diameter of internal threadD1Minor diameter of internal threadD2Pitch diameter of internal threaddExternal Major Diameterd1Minor diameter of external threadd2Pitch diameter of external threadnNumber of threds per Inch (TPI)PPitch (Distance)LLeadSNumber of StartshThread HeightFFlat WidthLELength of EngagmentαThread V half AngleAllowance, Deviation, and TolerancesTDTolerance - Minor diameter of internal thread & (Major Diameter)TD2Tolerance - Pitch diameter of internal threadTdTolerance - Minor diameter of external thread & (Major Diameter)Td2Tolerance - Minor diameter of external threadesAllowance - Pitch DiameterELAllowance - Major Diameter & (Minor Diameter)FormulasExternal Thread\( \begin{array}{l} \large d= \text{Diameter from designation} \\ \large n = \text{TPI from designation} \\ \large P = \frac{n}{TPI} \\ \large h = \frac{P}{2} \\ \large d _2= d\,-\,h \\ \large d_1 = d\,-\,P \\ \large F = 0.3707 \times P \\ \large 2\times\alpha = 29^{\circ} \\ \large \lambda = \tan^{-1} \left ( \frac{P \times S}{\pi \times d_2} \right ) \end{array} \)Internal thread\( \begin{array}{l} \large D= \text{Diameter from designation} \\ \large n = \text{TPI from designation} \\ \large P = \frac{n}{TPI} \\ \large h = \frac{P}{2} \\ \large D _2= D\,-\,h \\ \large D_1 = D\,-\,P \\ \large F = 0.3707 \times P \\ \large 2\times\alpha = 29^{\circ} \\ \large \lambda = \tan^{-1} \left ( \frac{P \times S}{\pi \times D_2} \right ) \end{array} \)Dimensions ChartClick the Thread Link to get the Full Thread Data for all classes in Inch and Metric units* Click icon to show Additional columns.(*) All dimensions are in InchesThreadMajor DiameterTPIPitchPitch DiameterMinor DiameterThread HeightFlat WidthLead AngleTap Drill Siuze1/4 - 16 ACME0.25160.06250.21880.18750.031250.02325.2°0.1875Metric Data ➢Tolerances ➢5/16 - 14 ACME0.3125140.07140.27680.24110.035710.02654.7°0.2411Metric Data ➢Tolerances ➢3/8 - 12 ACME0.375120.08330.33330.29170.041670.03094.55°0.2917Metric Data ➢Tolerances ➢7/16 - 12 ACME0.4375120.08330.39580.35420.041670.03093.83°0.3542Metric Data ➢Tolerances ➢1/2 - 10 ACME0.5100.10.450.40.050.03714.05°0.4Metric Data ➢Tolerances ➢5/8 - 8 ACME0.62580.1250.56250.50.06250.04634.05°0.5Metric Data ➢Tolerances ➢3/4 - 6 ACME0.7560.16670.66670.58330.083330.06184.55°0.5833Metric Data ➢Tolerances ➢7/8 - 6 ACME0.87560.16670.79170.70830.083330.06183.83°0.7083Metric Data ➢Tolerances ➢1 - 5 ACME150.20.90.80.10.07414.05°0.8Metric Data ➢Tolerances ➢1 1/8 - 5 ACME1.12550.21.0250.9250.10.07413.55°N/AMetric Data ➢Tolerances ➢1 1/4 - 5 ACME1.2550.21.151.050.10.07413.17°N/AMetric Data ➢Tolerances ➢1 3/8 - 4 ACME1.37540.251.251.1250.1250.09273.64°N/AMetric Data ➢Tolerances ➢1 1/2 - 4 ACME1.540.251.3751.250.1250.09273.31°N/AMetric Data ➢Tolerances ➢1 3/4 - 4 ACME1.7540.251.6251.50.1250.09272.8°N/AMetric Data ➢Tolerances ➢2 - 4 ACME240.251.8751.750.1250.09272.43°N/AMetric Data ➢Tolerances ➢2 1/4 - 3 ACME2.2530.33332.08331.91670.166670.12362.92°N/AMetric Data ➢Tolerances ➢2 1/2 - 3 ACME2.530.33332.33332.16670.166670.12362.6°N/AMetric Data ➢Tolerances ➢2 3/4 - 3 ACME2.7530.33332.58332.41670.166670.12362.35°N/AMetric Data ➢Tolerances ➢3 - 2 ACME320.52.752.50.250.18543.31°N/AMetric Data ➢Tolerances ➢3 1/2 - 2 ACME3.520.53.2530.250.18542.8°N/AMetric Data ➢Tolerances ➢4 - 2 ACME420.53.753.50.250.18542.43°N/AMetric Data ➢Tolerances ➢4 1/2 - 2 ACME4.520.54.2540.250.18542.14°N/AMetric Data ➢Tolerances ➢5 - 2 ACME520.54.754.50.250.18541.92°N/AMetric Data ➢Tolerances ➢ACME Threads – Limits of DimensionsTo manufacture or measure a thread, one has to know the maximum and minimum permissible values of the basic dimensions. These values are calculated according to the thread series and class (See below).Definition of terms:Allowance (Deviation): The minimum permissible distance between the basic and actual profile.Tolerance: The width of the tolerance field of a diameter on the actual thread profile. (Pitch, Major & Minor diameters)A small allowance means that the assembly of a male and female thread will be harder, but after assembly, there will be less freedom of movement.A large allowance means that the assembly of a male and female thread will be easier, but after assembly, there will be more freedom of movement.The allowance size does not influence a thread’s production difficulty or price.A wide tolerance is easier and cheaper to produce but yields a larger spread between threads.A narrow tolerance is challenging to produce and more expensive but yields a smaller spread between threads.Series & ClassesACME threads are divided into 3 series:G (General Purpose) – The most commonly used Acme threads. Wedging can occur under loads; therefore, it is recommended for applications where the screw and nut are supported individually.It has 3 precision classes 2G, 3G, and 4G.C (Centralized) – Tighter clearance between the internal and external threads. That prevents wedging on the flanks. More suitable for applications with higher load.It shares the exact basic dimensions of the C series. The difference is only in the tolerances.It has 3 precision classes 2C, 3C, and 4C.Stub – Compact threads with a 43% shorter stub height than standard Acme.Short and truncated thread profile, suitable for applications with limited space. Unlike G & C series, it only has a single precision class. They are defined in a separate ASTM document number B1.8.Series G & C have 3 preciosn classes:2G/2C – Least accurate and more commonly used.3G/3C – Medium accuracy.4G/4C – Highest accuracy, recommended to reduce backlash.Limits CalculationsASTM B1.5 defines how to calculate the tolerance of the following parameters:Major diameter (d / D)Minor diameter (d1 / D1)Pitch diameter (d2 / D2)Pitch & Lead (P / L)Angles between flanks (α)The below formulas are not valid for the following cases:Centralizes Acme series.Engagement lengths that are larger than twice the major diameter.Threads with multiple starts.TPI values that are not one of 2-6, 8, 10, 12, 14, or 16.Nominal diameters that are not one of 1/4, 5/16, 3/8, 7/16, 1/2, 3/4, 7/8, 1, 1-1/8, 1-1/4, 1-3/8, 1-1/2, 1-3/4, 2, 2-1/2, 2-3/4, 3, 3-1/2, 4, 4-1/2, or 5 Inches.For these cases, read the small print in ASTM B1.5 or use our Acme Thread Calculator  that handles all cases!Before calculating the limits, you need to obtain the following data:Allowance for major and minor diameters (el): Equals 0.002 for pitches of 10 TPI or coarser. For finer pitches, use 0.001.Allowance for pitch diameters (es): Should be obtained from ASM B1.5 (table 9). It cannot be calculated by a formula. You can either obtain it from the standard or use our below calculator.Payment options Pitch diameter tolerance (TD2): Should be obtained from ASM B1.5 (tables 5-7) or calculated with the below formula.\( TD_2 = K_P \times \sqrt{P} + K_D \times \sqrt{D} \)ClassKpKd2G / 3C0.030.0063G / 3C0.0140.00284G / 4C0.010.002Major diameter tolerance (Td): Equals to the TPI divided by 20. (But if less than 0.005, 0.005 should be used).After the above data has been obtained, you can proceed with the below formulas to calculate the limits. The below formulas are valid for all cases (Including The limitation listed above).Formulas for Limits of External Acme Thread\( \begin{array}{l} \large d_{max} = d_{nom} \\ \large d_{min} = d_{max}\,-\,T_d \\ \large d_{2\,max} = d_{2\,nom}\,-\,es \\ \large d_{2\,min} = d_{2\,max}\,-\,T_{d2} \\ \large d_{1\,max} = d_{1\,nom}\,-\,el \\ \large d_{1\,min} = d_{1\,max}\,-\,1.5 \times T_{d2} \end{array} \)Formulas for Limits of an Internal Acme Thread\( \begin{array}{l} \large D_{min} = D_{nom}\,+\,el \\ \large D_{max} = D_{min}\,+\,el \\ \large D_{2\,min} = D_{2\,nom} \\ \large D_{2\,max} = D_{2\,min}\,+\,T_{d2} \\ \large D_{1\,min} = D_{1\,nom} \\ \large D_{1\,max} = D_{1\,min}\,+\,T_{d} \end{array} \)Special ACME ThreadsBecause of the nature of its use cases and the limited list of standard configurations, special Acme threads are commonly used.What is considered a special Acme thread?A Diameter-Pitch combination that does not appear in this list.Multiple-Start threads.An engagement length that is larger than twice the major diameter.The Acme Thread Calculator  handles also Special Threads!Diameter-Pitch combinationsThe standard list of Acme threads in ASTM B1.5 has only one pitch option per diameter. However, “playing” with the pitch is an important design consideration since it allows us to increase the traverse speed by using a coarser pitch or increasing the accuracy by choosing a finer one. When opting for a special thread, ASTM B1.5 provides each pitch with the minimum and maximum allowed diameters.Premisable Diamter-Pitch CombinationsFor s thread with an intermediate pitch value, use the diameters shown for the next coarser pitch in the graph.To get the dimensions for such a thread, follow the formulas provided above or our Acme Thread Calculator, which knows how to handle any diameter-pitch combination.Multiple Start ThreadsMultiple-Start Acme threads are popular since they can bump up the traverse speed in multiples of 2, 3, 4, or more.The dimensions given in the standard are valid only for single-start threads. Use the below procedure to adjust the limits according to the number of starts.External threads (Screws) are not affected. The data for single-start threads should be used.For internal threads (Nuts), the allowance for major, minor, and pitch diameters is increased (relative to an equivalent single-start thread) by K x es. K depends on the number of starts: for 2 starts k=0.5, 3 starts k=0.75, and for 4 starts or more, k=1. Our Acme Thread Calculator also handles multiple-start threads!Length of EngagementIncreasing the length of the engagement means using a lengthier nut that can support higher forces. The data listed in ASTM B1.5 and the formulas given above are valid for engagement lengths up to twice the major diameter. The pitch diameter allowance (es) should be increased by 0.1 x es x (LE -  2 x d) when LE>2XD. Our Acme Thread Calculator also handles all engagement lengths.Related Glossary Terms:Lead (Threading)CNC MachineMajor DiameterTooth per inch (tpi)Thread Allowance (es)Minor DiameterPitch DiameterPitchThread Height (Depth)Tap Drill Size

(*) All dimensions are in InchesThreadMajor DiameterTPIPitchPitch DiameterMinor DiameterThread HeightFlat WidthLead AngleTap Drill Siuze1/4 - 16 ACME0.25160.06250.21880.18750.031250.02325.2°0.1875Metric Data ➢Tolerances ➢5/16 - 14 ACME0.3125140.07140.27680.24110.035710.02654.7°0.2411Metric Data ➢Tolerances ➢3/8 - 12 ACME0.375120.08330.33330.29170.041670.03094.55°0.2917Metric Data ➢Tolerances ➢7/16 - 12 ACME0.4375120.08330.39580.35420.041670.03093.83°0.3542Metric Data ➢Tolerances ➢1/2 - 10 ACME0.5100.10.450.40.050.03714.05°0.4Metric Data ➢Tolerances ➢5/8 - 8 ACME0.62580.1250.56250.50.06250.04634.05°0.5Metric Data ➢Tolerances ➢3/4 - 6 ACME0.7560.16670.66670.58330.083330.06184.55°0.5833Metric Data ➢Tolerances ➢7/8 - 6 ACME0.87560.16670.79170.70830.083330.06183.83°0.7083Metric Data ➢Tolerances ➢1 - 5 ACME150.20.90.80.10.07414.05°0.8Metric Data ➢Tolerances ➢1 1/8 - 5 ACME1.12550.21.0250.9250.10.07413.55°N/AMetric Data ➢Tolerances ➢1 1/4 - 5 ACME1.2550.21.151.050.10.07413.17°N/AMetric Data ➢Tolerances ➢1 3/8 - 4 ACME1.37540.251.251.1250.1250.09273.64°N/AMetric Data ➢Tolerances ➢1 1/2 - 4 ACME1.540.251.3751.250.1250.09273.31°N/AMetric Data ➢Tolerances ➢1 3/4 - 4 ACME1.7540.251.6251.50.1250.09272.8°N/AMetric Data ➢Tolerances ➢2 - 4 ACME240.251.8751.750.1250.09272.43°N/AMetric Data ➢Tolerances ➢2 1/4 - 3 ACME2.2530.33332.08331.91670.166670.12362.92°N/AMetric Data ➢Tolerances ➢2 1/2 - 3 ACME2.530.33332.33332.16670.166670.12362.6°N/AMetric Data ➢Tolerances ➢2 3/4 - 3 ACME2.7530.33332.58332.41670.166670.12362.35°N/AMetric Data ➢Tolerances ➢3 - 2 ACME320.52.752.50.250.18543.31°N/AMetric Data ➢Tolerances ➢3 1/2 - 2 ACME3.520.53.2530.250.18542.8°N/AMetric Data ➢Tolerances ➢4 - 2 ACME420.53.753.50.250.18542.43°N/AMetric Data ➢Tolerances ➢4 1/2 - 2 ACME4.520.54.2540.250.18542.14°N/AMetric Data ➢Tolerances ➢5 - 2 ACME520.54.754.50.250.18541.92°N/AMetric Data ➢Tolerances ➢ACME Threads – Limits of DimensionsTo manufacture or measure a thread, one has to know the maximum and minimum permissible values of the basic dimensions. These values are calculated according to the thread series and class (See below).Definition of terms:Allowance (Deviation): The minimum permissible distance between the basic and actual profile.Tolerance: The width of the tolerance field of a diameter on the actual thread profile. (Pitch, Major & Minor diameters)A small allowance means that the assembly of a male and female thread will be harder, but after assembly, there will be less freedom of movement.A large allowance means that the assembly of a male and female thread will be easier, but after assembly, there will be more freedom of movement.The allowance size does not influence a thread’s production difficulty or price.A wide tolerance is easier and cheaper to produce but yields a larger spread between threads.A narrow tolerance is challenging to produce and more expensive but yields a smaller spread between threads.Series & ClassesACME threads are divided into 3 series:G (General Purpose) – The most commonly used Acme threads. Wedging can occur under loads; therefore, it is recommended for applications where the screw and nut are supported individually.It has 3 precision classes 2G, 3G, and 4G.C (Centralized) – Tighter clearance between the internal and external threads. That prevents wedging on the flanks. More suitable for applications with higher load.It shares the exact basic dimensions of the C series. The difference is only in the tolerances.It has 3 precision classes 2C, 3C, and 4C.Stub – Compact threads with a 43% shorter stub height than standard Acme.Short and truncated thread profile, suitable for applications with limited space. Unlike G & C series, it only has a single precision class. They are defined in a separate ASTM document number B1.8.Series G & C have 3 preciosn classes:2G/2C – Least accurate and more commonly used.3G/3C – Medium accuracy.4G/4C – Highest accuracy, recommended to reduce backlash.Limits CalculationsASTM B1.5 defines how to calculate the tolerance of the following parameters:Major diameter (d / D)Minor diameter (d1 / D1)Pitch diameter (d2 / D2)Pitch & Lead (P / L)Angles between flanks (α)The below formulas are not valid for the following cases:Centralizes Acme series.Engagement lengths that are larger than twice the major diameter.Threads with multiple starts.TPI values that are not one of 2-6, 8, 10, 12, 14, or 16.Nominal diameters that are not one of 1/4, 5/16, 3/8, 7/16, 1/2, 3/4, 7/8, 1, 1-1/8, 1-1/4, 1-3/8, 1-1/2, 1-3/4, 2, 2-1/2, 2-3/4, 3, 3-1/2, 4, 4-1/2, or 5 Inches.For these cases, read the small print in ASTM B1.5 or use our Acme Thread Calculator  that handles all cases!Before calculating the limits, you need to obtain the following data:Allowance for major and minor diameters (el): Equals 0.002 for pitches of 10 TPI or coarser. For finer pitches, use 0.001.Allowance for pitch diameters (es): Should be obtained from ASM B1.5 (table 9). It cannot be calculated by a formula. You can either obtain it from the standard or use our below calculator.Payment options Pitch diameter tolerance (TD2): Should be obtained from ASM B1.5 (tables 5-7) or calculated with the below formula.\( TD_2 = K_P \times \sqrt{P} + K_D \times \sqrt{D} \)ClassKpKd2G / 3C0.030.0063G / 3C0.0140.00284G / 4C0.010.002Major diameter tolerance (Td): Equals to the TPI divided by 20. (But if less than 0.005, 0.005 should be used).After the above data has been obtained, you can proceed with the below formulas to calculate the limits. The below formulas are valid for all cases (Including The limitation listed above).Formulas for Limits of External Acme Thread\( \begin{array}{l} \large d_{max} = d_{nom} \\ \large d_{min} = d_{max}\,-\,T_d \\ \large d_{2\,max} = d_{2\,nom}\,-\,es \\ \large d_{2\,min} = d_{2\,max}\,-\,T_{d2} \\ \large d_{1\,max} = d_{1\,nom}\,-\,el \\ \large d_{1\,min} = d_{1\,max}\,-\,1.5 \times T_{d2} \end{array} \)Formulas for Limits of an Internal Acme Thread\( \begin{array}{l} \large D_{min} = D_{nom}\,+\,el \\ \large D_{max} = D_{min}\,+\,el \\ \large D_{2\,min} = D_{2\,nom} \\ \large D_{2\,max} = D_{2\,min}\,+\,T_{d2} \\ \large D_{1\,min} = D_{1\,nom} \\ \large D_{1\,max} = D_{1\,min}\,+\,T_{d} \end{array} \)Special ACME ThreadsBecause of the nature of its use cases and the limited list of standard configurations, special Acme threads are commonly used.What is considered a special Acme thread?A Diameter-Pitch combination that does not appear in this list.Multiple-Start threads.An engagement length that is larger than twice the major diameter.The Acme Thread Calculator  handles also Special Threads!Diameter-Pitch combinationsThe standard list of Acme threads in ASTM B1.5 has only one pitch option per diameter. However, “playing” with the pitch is an important design consideration since it allows us to increase the traverse speed by using a coarser pitch or increasing the accuracy by choosing a finer one. When opting for a special thread, ASTM B1.5 provides each pitch with the minimum and maximum allowed diameters.Premisable Diamter-Pitch CombinationsFor s thread with an intermediate pitch value, use the diameters shown for the next coarser pitch in the graph.To get the dimensions for such a thread, follow the formulas provided above or our Acme Thread Calculator, which knows how to handle any diameter-pitch combination.Multiple Start ThreadsMultiple-Start Acme threads are popular since they can bump up the traverse speed in multiples of 2, 3, 4, or more.The dimensions given in the standard are valid only for single-start threads. Use the below procedure to adjust the limits according to the number of starts.External threads (Screws) are not affected. The data for single-start threads should be used.For internal threads (Nuts), the allowance for major, minor, and pitch diameters is increased (relative to an equivalent single-start thread) by K x es. K depends on the number of starts: for 2 starts k=0.5, 3 starts k=0.75, and for 4 starts or more, k=1. Our Acme Thread Calculator also handles multiple-start threads!Length of EngagementIncreasing the length of the engagement means using a lengthier nut that can support higher forces. The data listed in ASTM B1.5 and the formulas given above are valid for engagement lengths up to twice the major diameter. The pitch diameter allowance (es) should be increased by 0.1 x es x (LE -  2 x d) when LE>2XD. Our Acme Thread Calculator also handles all engagement lengths.Related Glossary Terms:Lead (Threading)CNC MachineMajor DiameterTooth per inch (tpi)Thread Allowance (es)Minor DiameterPitch DiameterPitchThread Height (Depth)Tap Drill Size

Acme threadChart PDF

Series:G – General use.C – Centralized. This class defines a more restricted clearance at the major diameter of both the internal and external screws that prevent wedging on the flanks.Class:The class is defined by a number between 2 and 4.2– Lower precision.4 – Higher precision.Internal and external designations are exactly the same. You cannot tell from the description alone if the thread is external or internal.Additional Parameters:Direction: By default, the thread is right-hand. For a left-hand thread, add the suffix -LH.Number of Starts: By default, all threads have a single start. Thus, the lead equals the pitch. For a multiple-start thread, the lead is also indicated by the letter L. For example, 1/4– 0.0625P – 0.1875L-ACMEdenotes a 0.25″ ACME thread with 3 starts. (0.1875/0.0625=3)Designation Examples of Acme ThreadsDesignationSeriesNominalDiameterTPIPitchLeadClassNumber of StartsThread Direction1/2-10-ACME 2GG0.5"100.1"=Pitch21Right Hand0.5-10-ACME 4CC0.5"100.1"=Pitch41Right Hand1/4– 0.0625P – 0.1875L-ACME 2GG0.25"160.0625"0.1875"23Right Hand2.5-3-ACME 4C-LHC2.5"30.3333"=Pitch41Left HandACME Threads – Basic DimensionsThe basic dimensions are nominal dimensions of the ACME profile without allowances and tolerances (The series and class define that – see below). They are based on standard ASTM B1.5. The basic dimensions can be used for design. However, for manufacturing and machining, you need the allowable range of each dimension. This data can be found in the ASTM standard or in the Limits and Dimensions section below. All the basic dimensions are derived from simple formulas based on the thread’s nominal diameter and pitch.SymbolsList of symbols used in charts and formulas of ACME ThreadsSymbolExplanationBasic Parameters - Diameters and PitchDMajor (Basic) diameter of internal threadD1Minor diameter of internal threadD2Pitch diameter of internal threaddExternal Major Diameterd1Minor diameter of external threadd2Pitch diameter of external threadnNumber of threds per Inch (TPI)PPitch (Distance)LLeadSNumber of StartshThread HeightFFlat WidthLELength of EngagmentαThread V half AngleAllowance, Deviation, and TolerancesTDTolerance - Minor diameter of internal thread & (Major Diameter)TD2Tolerance - Pitch diameter of internal threadTdTolerance - Minor diameter of external thread & (Major Diameter)Td2Tolerance - Minor diameter of external threadesAllowance - Pitch DiameterELAllowance - Major Diameter & (Minor Diameter)FormulasExternal Thread\( \begin{array}{l} \large d= \text{Diameter from designation} \\ \large n = \text{TPI from designation} \\ \large P = \frac{n}{TPI} \\ \large h = \frac{P}{2} \\ \large d _2= d\,-\,h \\ \large d_1 = d\,-\,P \\ \large F = 0.3707 \times P \\ \large 2\times\alpha = 29^{\circ} \\ \large \lambda = \tan^{-1} \left ( \frac{P \times S}{\pi \times d_2} \right ) \end{array} \)Internal thread\( \begin{array}{l} \large D= \text{Diameter from designation} \\ \large n = \text{TPI from designation} \\ \large P = \frac{n}{TPI} \\ \large h = \frac{P}{2} \\ \large D _2= D\,-\,h \\ \large D_1 = D\,-\,P \\ \large F = 0.3707 \times P \\ \large 2\times\alpha = 29^{\circ} \\ \large \lambda = \tan^{-1} \left ( \frac{P \times S}{\pi \times D_2} \right ) \end{array} \)Dimensions ChartClick the Thread Link to get the Full Thread Data for all classes in Inch and Metric units* Click icon to show Additional columns.(*) All dimensions are in InchesThreadMajor DiameterTPIPitchPitch DiameterMinor DiameterThread HeightFlat WidthLead AngleTap Drill Siuze1/4 - 16 ACME0.25160.06250.21880.18750.031250.02325.2°0.1875Metric Data ➢Tolerances ➢5/16 - 14 ACME0.3125140.07140.27680.24110.035710.02654.7°0.2411Metric Data ➢Tolerances ➢3/8 - 12 ACME0.375120.08330.33330.29170.041670.03094.55°0.2917Metric Data ➢Tolerances ➢7/16 - 12 ACME0.4375120.08330.39580.35420.041670.03093.83°0.3542Metric Data ➢Tolerances ➢1/2 - 10 ACME0.5100.10.450.40.050.03714.05°0.4Metric Data ➢Tolerances ➢5/8 - 8 ACME0.62580.1250.56250.50.06250.04634.05°0.5Metric Data ➢Tolerances ➢3/4 - 6 ACME0.7560.16670.66670.58330.083330.06184.55°0.5833Metric Data ➢Tolerances ➢7/8 - 6 ACME0.87560.16670.79170.70830.083330.06183.83°0.7083Metric Data ➢Tolerances ➢1 - 5 ACME150.20.90.80.10.07414.05°0.8Metric Data ➢Tolerances ➢1 1/8 - 5 ACME1.12550.21.0250.9250.10.07413.55°N/AMetric Data ➢Tolerances ➢1 1/4 - 5 ACME1.2550.21.151.050.10.07413.17°N/AMetric Data ➢Tolerances ➢1 3/8 - 4 ACME1.37540.251.251.1250.1250.09273.64°N/AMetric Data ➢Tolerances ➢1 1/2 - 4 ACME1.540.251.3751.250.1250.09273.31°N/AMetric Data ➢Tolerances ➢1 3/4 - 4 ACME1.7540.251.6251.50.1250.09272.8°N/AMetric Data ➢Tolerances ➢2 - 4 ACME240.251.8751.750.1250.09272.43°N/AMetric Data ➢Tolerances ➢2 1/4 - 3 ACME2.2530.33332.08331.91670.166670.12362.92°N/AMetric Data ➢Tolerances ➢2 1/2 - 3 ACME2.530.33332.33332.16670.166670.12362.6°N/AMetric Data ➢Tolerances ➢2 3/4 - 3 ACME2.7530.33332.58332.41670.166670.12362.35°N/AMetric Data ➢Tolerances ➢3 - 2 ACME320.52.752.50.250.18543.31°N/AMetric Data ➢Tolerances ➢3 1/2 - 2 ACME3.520.53.2530.250.18542.8°N/AMetric Data ➢Tolerances ➢4 - 2 ACME420.53.753.50.250.18542.43°N/AMetric Data ➢Tolerances ➢4 1/2 - 2 ACME4.520.54.2540.250.18542.14°N/AMetric Data ➢Tolerances ➢5 - 2 ACME520.54.754.50.250.18541.92°N/AMetric Data ➢Tolerances ➢ACME Threads – Limits of DimensionsTo manufacture or measure a thread, one has to know the maximum and minimum permissible values of the basic dimensions. These values are calculated according to the thread series and class (See below).Definition of terms:Allowance (Deviation): The minimum permissible distance between the basic and actual profile.Tolerance: The width of the tolerance field of a diameter on the actual thread profile. (Pitch, Major & Minor diameters)A small allowance means that the assembly of a male and female thread will be harder, but after assembly, there will be less freedom of movement.A large allowance means that the assembly of a male and female thread will be easier, but after assembly, there will be more freedom of movement.The allowance size does not influence a thread’s production difficulty or price.A wide tolerance is easier and cheaper to produce but yields a larger spread between threads.A narrow tolerance is challenging to produce and more expensive but yields a smaller spread between threads.Series & ClassesACME threads are divided into 3 series:G (General Purpose) – The most commonly used Acme threads. Wedging can occur under loads; therefore, it is recommended for applications where the screw and nut are supported individually.It has 3 precision classes 2G, 3G, and 4G.C (Centralized) – Tighter clearance between the internal and external threads. That prevents wedging on the flanks. More suitable for applications with higher load.It shares the exact basic dimensions of the C series. The difference is only in the tolerances.It has 3 precision classes 2C, 3C, and 4C.Stub – Compact threads with a 43% shorter stub height than standard Acme.Short and truncated thread profile, suitable for applications with limited space. Unlike G & C series, it only has a single precision class. They are defined in a separate ASTM document number B1.8.Series G & C have 3 preciosn classes:2G/2C – Least accurate and more commonly used.3G/3C – Medium accuracy.4G/4C – Highest accuracy, recommended to reduce backlash.Limits CalculationsASTM B1.5 defines how to calculate the tolerance of the following parameters:Major diameter (d / D)Minor diameter (d1 / D1)Pitch diameter (d2 / D2)Pitch & Lead (P / L)Angles between flanks (α)The below formulas are not valid for the following cases:Centralizes Acme series.Engagement lengths that are larger than twice the major diameter.Threads with multiple starts.TPI values that are not one of 2-6, 8, 10, 12, 14, or 16.Nominal diameters that are not one of 1/4, 5/16, 3/8, 7/16, 1/2, 3/4, 7/8, 1, 1-1/8, 1-1/4, 1-3/8, 1-1/2, 1-3/4, 2, 2-1/2, 2-3/4, 3, 3-1/2, 4, 4-1/2, or 5 Inches.For these cases, read the small print in ASTM B1.5 or use our Acme Thread Calculator  that handles all cases!Before calculating the limits, you need to obtain the following data:Allowance for major and minor diameters (el): Equals 0.002 for pitches of 10 TPI or coarser. For finer pitches, use 0.001.Allowance for pitch diameters (es): Should be obtained from ASM B1.5 (table 9). It cannot be calculated by a formula. You can either obtain it from the standard or use our below calculator.Payment options Pitch diameter tolerance (TD2): Should be obtained from ASM B1.5 (tables 5-7) or calculated with the below formula.\( TD_2 = K_P \times \sqrt{P} + K_D \times \sqrt{D} \)ClassKpKd2G / 3C0.030.0063G / 3C0.0140.00284G / 4C0.010.002Major diameter tolerance (Td): Equals to the TPI divided by 20. (But if less than 0.005, 0.005 should be used).After the above data has been obtained, you can proceed with the below formulas to calculate the limits. The below formulas are valid for all cases (Including The limitation listed above).Formulas for Limits of External Acme Thread\( \begin{array}{l} \large d_{max} = d_{nom} \\ \large d_{min} = d_{max}\,-\,T_d \\ \large d_{2\,max} = d_{2\,nom}\,-\,es \\ \large d_{2\,min} = d_{2\,max}\,-\,T_{d2} \\ \large d_{1\,max} = d_{1\,nom}\,-\,el \\ \large d_{1\,min} = d_{1\,max}\,-\,1.5 \times T_{d2} \end{array} \)Formulas for Limits of an Internal Acme Thread\( \begin{array}{l} \large D_{min} = D_{nom}\,+\,el \\ \large D_{max} = D_{min}\,+\,el \\ \large D_{2\,min} = D_{2\,nom} \\ \large D_{2\,max} = D_{2\,min}\,+\,T_{d2} \\ \large D_{1\,min} = D_{1\,nom} \\ \large D_{1\,max} = D_{1\,min}\,+\,T_{d} \end{array} \)Special ACME ThreadsBecause of the nature of its use cases and the limited list of standard configurations, special Acme threads are commonly used.What is considered a special Acme thread?A Diameter-Pitch combination that does not appear in this list.Multiple-Start threads.An engagement length that is larger than twice the major diameter.The Acme Thread Calculator  handles also Special Threads!Diameter-Pitch combinationsThe standard list of Acme threads in ASTM B1.5 has only one pitch option per diameter. However, “playing” with the pitch is an important design consideration since it allows us to increase the traverse speed by using a coarser pitch or increasing the accuracy by choosing a finer one. When opting for a special thread, ASTM B1.5 provides each pitch with the minimum and maximum allowed diameters.Premisable Diamter-Pitch CombinationsFor s thread with an intermediate pitch value, use the diameters shown for the next coarser pitch in the graph.To get the dimensions for such a thread, follow the formulas provided above or our Acme Thread Calculator, which knows how to handle any diameter-pitch combination.Multiple Start ThreadsMultiple-Start Acme threads are popular since they can bump up the traverse speed in multiples of 2, 3, 4, or more.The dimensions given in the standard are valid only for single-start threads. Use the below procedure to adjust the limits according to the number of starts.External threads (Screws) are not affected. The data for single-start threads should be used.For internal threads (Nuts), the allowance for major, minor, and pitch diameters is increased (relative to an equivalent single-start thread) by K x es. K depends on the number of starts: for 2 starts k=0.5, 3 starts k=0.75, and for 4 starts or more, k=1. Our Acme Thread Calculator also handles multiple-start threads!Length of EngagementIncreasing the length of the engagement means using a lengthier nut that can support higher forces. The data listed in ASTM B1.5 and the formulas given above are valid for engagement lengths up to twice the major diameter. The pitch diameter allowance (es) should be increased by 0.1 x es x (LE -  2 x d) when LE>2XD. Our Acme Thread Calculator also handles all engagement lengths.Related Glossary Terms:Lead (Threading)CNC MachineMajor DiameterTooth per inch (tpi)Thread Allowance (es)Minor DiameterPitch DiameterPitchThread Height (Depth)Tap Drill Size

Pitch:By default, the pitch is given in TPI. For example, 1/4-20 means a thread with a pitch of 20 TPI (1/20=0.05″).On multiple starts threads (see below), the pitch is indicated by distance. For example, 1/4-0.05P means a thread with a pitch of 0.05″ (same as 20 TPI).Series:G – General use.C – Centralized. This class defines a more restricted clearance at the major diameter of both the internal and external screws that prevent wedging on the flanks.Class:The class is defined by a number between 2 and 4.2– Lower precision.4 – Higher precision.Internal and external designations are exactly the same. You cannot tell from the description alone if the thread is external or internal.Additional Parameters:Direction: By default, the thread is right-hand. For a left-hand thread, add the suffix -LH.Number of Starts: By default, all threads have a single start. Thus, the lead equals the pitch. For a multiple-start thread, the lead is also indicated by the letter L. For example, 1/4– 0.0625P – 0.1875L-ACMEdenotes a 0.25″ ACME thread with 3 starts. (0.1875/0.0625=3)Designation Examples of Acme ThreadsDesignationSeriesNominalDiameterTPIPitchLeadClassNumber of StartsThread Direction1/2-10-ACME 2GG0.5"100.1"=Pitch21Right Hand0.5-10-ACME 4CC0.5"100.1"=Pitch41Right Hand1/4– 0.0625P – 0.1875L-ACME 2GG0.25"160.0625"0.1875"23Right Hand2.5-3-ACME 4C-LHC2.5"30.3333"=Pitch41Left HandACME Threads – Basic DimensionsThe basic dimensions are nominal dimensions of the ACME profile without allowances and tolerances (The series and class define that – see below). They are based on standard ASTM B1.5. The basic dimensions can be used for design. However, for manufacturing and machining, you need the allowable range of each dimension. This data can be found in the ASTM standard or in the Limits and Dimensions section below. All the basic dimensions are derived from simple formulas based on the thread’s nominal diameter and pitch.SymbolsList of symbols used in charts and formulas of ACME ThreadsSymbolExplanationBasic Parameters - Diameters and PitchDMajor (Basic) diameter of internal threadD1Minor diameter of internal threadD2Pitch diameter of internal threaddExternal Major Diameterd1Minor diameter of external threadd2Pitch diameter of external threadnNumber of threds per Inch (TPI)PPitch (Distance)LLeadSNumber of StartshThread HeightFFlat WidthLELength of EngagmentαThread V half AngleAllowance, Deviation, and TolerancesTDTolerance - Minor diameter of internal thread & (Major Diameter)TD2Tolerance - Pitch diameter of internal threadTdTolerance - Minor diameter of external thread & (Major Diameter)Td2Tolerance - Minor diameter of external threadesAllowance - Pitch DiameterELAllowance - Major Diameter & (Minor Diameter)FormulasExternal Thread\( \begin{array}{l} \large d= \text{Diameter from designation} \\ \large n = \text{TPI from designation} \\ \large P = \frac{n}{TPI} \\ \large h = \frac{P}{2} \\ \large d _2= d\,-\,h \\ \large d_1 = d\,-\,P \\ \large F = 0.3707 \times P \\ \large 2\times\alpha = 29^{\circ} \\ \large \lambda = \tan^{-1} \left ( \frac{P \times S}{\pi \times d_2} \right ) \end{array} \)Internal thread\( \begin{array}{l} \large D= \text{Diameter from designation} \\ \large n = \text{TPI from designation} \\ \large P = \frac{n}{TPI} \\ \large h = \frac{P}{2} \\ \large D _2= D\,-\,h \\ \large D_1 = D\,-\,P \\ \large F = 0.3707 \times P \\ \large 2\times\alpha = 29^{\circ} \\ \large \lambda = \tan^{-1} \left ( \frac{P \times S}{\pi \times D_2} \right ) \end{array} \)Dimensions ChartClick the Thread Link to get the Full Thread Data for all classes in Inch and Metric units* Click icon to show Additional columns.(*) All dimensions are in InchesThreadMajor DiameterTPIPitchPitch DiameterMinor DiameterThread HeightFlat WidthLead AngleTap Drill Siuze1/4 - 16 ACME0.25160.06250.21880.18750.031250.02325.2°0.1875Metric Data ➢Tolerances ➢5/16 - 14 ACME0.3125140.07140.27680.24110.035710.02654.7°0.2411Metric Data ➢Tolerances ➢3/8 - 12 ACME0.375120.08330.33330.29170.041670.03094.55°0.2917Metric Data ➢Tolerances ➢7/16 - 12 ACME0.4375120.08330.39580.35420.041670.03093.83°0.3542Metric Data ➢Tolerances ➢1/2 - 10 ACME0.5100.10.450.40.050.03714.05°0.4Metric Data ➢Tolerances ➢5/8 - 8 ACME0.62580.1250.56250.50.06250.04634.05°0.5Metric Data ➢Tolerances ➢3/4 - 6 ACME0.7560.16670.66670.58330.083330.06184.55°0.5833Metric Data ➢Tolerances ➢7/8 - 6 ACME0.87560.16670.79170.70830.083330.06183.83°0.7083Metric Data ➢Tolerances ➢1 - 5 ACME150.20.90.80.10.07414.05°0.8Metric Data ➢Tolerances ➢1 1/8 - 5 ACME1.12550.21.0250.9250.10.07413.55°N/AMetric Data ➢Tolerances ➢1 1/4 - 5 ACME1.2550.21.151.050.10.07413.17°N/AMetric Data ➢Tolerances ➢1 3/8 - 4 ACME1.37540.251.251.1250.1250.09273.64°N/AMetric Data ➢Tolerances ➢1 1/2 - 4 ACME1.540.251.3751.250.1250.09273.31°N/AMetric Data ➢Tolerances ➢1 3/4 - 4 ACME1.7540.251.6251.50.1250.09272.8°N/AMetric Data ➢Tolerances ➢2 - 4 ACME240.251.8751.750.1250.09272.43°N/AMetric Data ➢Tolerances ➢2 1/4 - 3 ACME2.2530.33332.08331.91670.166670.12362.92°N/AMetric Data ➢Tolerances ➢2 1/2 - 3 ACME2.530.33332.33332.16670.166670.12362.6°N/AMetric Data ➢Tolerances ➢2 3/4 - 3 ACME2.7530.33332.58332.41670.166670.12362.35°N/AMetric Data ➢Tolerances ➢3 - 2 ACME320.52.752.50.250.18543.31°N/AMetric Data ➢Tolerances ➢3 1/2 - 2 ACME3.520.53.2530.250.18542.8°N/AMetric Data ➢Tolerances ➢4 - 2 ACME420.53.753.50.250.18542.43°N/AMetric Data ➢Tolerances ➢4 1/2 - 2 ACME4.520.54.2540.250.18542.14°N/AMetric Data ➢Tolerances ➢5 - 2 ACME520.54.754.50.250.18541.92°N/AMetric Data ➢Tolerances ➢ACME Threads – Limits of DimensionsTo manufacture or measure a thread, one has to know the maximum and minimum permissible values of the basic dimensions. These values are calculated according to the thread series and class (See below).Definition of terms:Allowance (Deviation): The minimum permissible distance between the basic and actual profile.Tolerance: The width of the tolerance field of a diameter on the actual thread profile. (Pitch, Major & Minor diameters)A small allowance means that the assembly of a male and female thread will be harder, but after assembly, there will be less freedom of movement.A large allowance means that the assembly of a male and female thread will be easier, but after assembly, there will be more freedom of movement.The allowance size does not influence a thread’s production difficulty or price.A wide tolerance is easier and cheaper to produce but yields a larger spread between threads.A narrow tolerance is challenging to produce and more expensive but yields a smaller spread between threads.Series & ClassesACME threads are divided into 3 series:G (General Purpose) – The most commonly used Acme threads. Wedging can occur under loads; therefore, it is recommended for applications where the screw and nut are supported individually.It has 3 precision classes 2G, 3G, and 4G.C (Centralized) – Tighter clearance between the internal and external threads. That prevents wedging on the flanks. More suitable for applications with higher load.It shares the exact basic dimensions of the C series. The difference is only in the tolerances.It has 3 precision classes 2C, 3C, and 4C.Stub – Compact threads with a 43% shorter stub height than standard Acme.Short and truncated thread profile, suitable for applications with limited space. Unlike G & C series, it only has a single precision class. They are defined in a separate ASTM document number B1.8.Series G & C have 3 preciosn classes:2G/2C – Least accurate and more commonly used.3G/3C – Medium accuracy.4G/4C – Highest accuracy, recommended to reduce backlash.Limits CalculationsASTM B1.5 defines how to calculate the tolerance of the following parameters:Major diameter (d / D)Minor diameter (d1 / D1)Pitch diameter (d2 / D2)Pitch & Lead (P / L)Angles between flanks (α)The below formulas are not valid for the following cases:Centralizes Acme series.Engagement lengths that are larger than twice the major diameter.Threads with multiple starts.TPI values that are not one of 2-6, 8, 10, 12, 14, or 16.Nominal diameters that are not one of 1/4, 5/16, 3/8, 7/16, 1/2, 3/4, 7/8, 1, 1-1/8, 1-1/4, 1-3/8, 1-1/2, 1-3/4, 2, 2-1/2, 2-3/4, 3, 3-1/2, 4, 4-1/2, or 5 Inches.For these cases, read the small print in ASTM B1.5 or use our Acme Thread Calculator  that handles all cases!Before calculating the limits, you need to obtain the following data:Allowance for major and minor diameters (el): Equals 0.002 for pitches of 10 TPI or coarser. For finer pitches, use 0.001.Allowance for pitch diameters (es): Should be obtained from ASM B1.5 (table 9). It cannot be calculated by a formula. You can either obtain it from the standard or use our below calculator.Payment options Pitch diameter tolerance (TD2): Should be obtained from ASM B1.5 (tables 5-7) or calculated with the below formula.\( TD_2 = K_P \times \sqrt{P} + K_D \times \sqrt{D} \)ClassKpKd2G / 3C0.030.0063G / 3C0.0140.00284G / 4C0.010.002Major diameter tolerance (Td): Equals to the TPI divided by 20. (But if less than 0.005, 0.005 should be used).After the above data has been obtained, you can proceed with the below formulas to calculate the limits. The below formulas are valid for all cases (Including The limitation listed above).Formulas for Limits of External Acme Thread\( \begin{array}{l} \large d_{max} = d_{nom} \\ \large d_{min} = d_{max}\,-\,T_d \\ \large d_{2\,max} = d_{2\,nom}\,-\,es \\ \large d_{2\,min} = d_{2\,max}\,-\,T_{d2} \\ \large d_{1\,max} = d_{1\,nom}\,-\,el \\ \large d_{1\,min} = d_{1\,max}\,-\,1.5 \times T_{d2} \end{array} \)Formulas for Limits of an Internal Acme Thread\( \begin{array}{l} \large D_{min} = D_{nom}\,+\,el \\ \large D_{max} = D_{min}\,+\,el \\ \large D_{2\,min} = D_{2\,nom} \\ \large D_{2\,max} = D_{2\,min}\,+\,T_{d2} \\ \large D_{1\,min} = D_{1\,nom} \\ \large D_{1\,max} = D_{1\,min}\,+\,T_{d} \end{array} \)Special ACME ThreadsBecause of the nature of its use cases and the limited list of standard configurations, special Acme threads are commonly used.What is considered a special Acme thread?A Diameter-Pitch combination that does not appear in this list.Multiple-Start threads.An engagement length that is larger than twice the major diameter.The Acme Thread Calculator  handles also Special Threads!Diameter-Pitch combinationsThe standard list of Acme threads in ASTM B1.5 has only one pitch option per diameter. However, “playing” with the pitch is an important design consideration since it allows us to increase the traverse speed by using a coarser pitch or increasing the accuracy by choosing a finer one. When opting for a special thread, ASTM B1.5 provides each pitch with the minimum and maximum allowed diameters.Premisable Diamter-Pitch CombinationsFor s thread with an intermediate pitch value, use the diameters shown for the next coarser pitch in the graph.To get the dimensions for such a thread, follow the formulas provided above or our Acme Thread Calculator, which knows how to handle any diameter-pitch combination.Multiple Start ThreadsMultiple-Start Acme threads are popular since they can bump up the traverse speed in multiples of 2, 3, 4, or more.The dimensions given in the standard are valid only for single-start threads. Use the below procedure to adjust the limits according to the number of starts.External threads (Screws) are not affected. The data for single-start threads should be used.For internal threads (Nuts), the allowance for major, minor, and pitch diameters is increased (relative to an equivalent single-start thread) by K x es. K depends on the number of starts: for 2 starts k=0.5, 3 starts k=0.75, and for 4 starts or more, k=1. Our Acme Thread Calculator also handles multiple-start threads!Length of EngagementIncreasing the length of the engagement means using a lengthier nut that can support higher forces. The data listed in ASTM B1.5 and the formulas given above are valid for engagement lengths up to twice the major diameter. The pitch diameter allowance (es) should be increased by 0.1 x es x (LE -  2 x d) when LE>2XD. Our Acme Thread Calculator also handles all engagement lengths.Related Glossary Terms:Lead (Threading)CNC MachineMajor DiameterTooth per inch (tpi)Thread Allowance (es)Minor DiameterPitch DiameterPitchThread Height (Depth)Tap Drill Size

A ring main distribution system provides more reliable, maintainable, and balanced power distribution compared to a radial configuration.

Acme threadchart

Increasing the length of the engagement means using a lengthier nut that can support higher forces. The data listed in ASTM B1.5 and the formulas given above are valid for engagement lengths up to twice the major diameter. The pitch diameter allowance (es) should be increased by 0.1 x es x (LE -  2 x d) when LE>2XD. Our Acme Thread Calculator also handles all engagement lengths.Related Glossary Terms:Lead (Threading)CNC MachineMajor DiameterTooth per inch (tpi)Thread Allowance (es)Minor DiameterPitch DiameterPitchThread Height (Depth)Tap Drill Size

ACME threadChart mm

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Basic designation syntax:Nominal Diameter in Inch FractionPitch in TPISeries: G – General / C – CentralizedClass: 2, 3, or 4. Indicates the precision.

Ring main distribution systems are commonly employed for medium to high power distribution requirements in the following scenarios:

Acme threadtypes

Internal and external designations are exactly the same. You cannot tell from the description alone if the thread is external or internal.Additional Parameters:Direction: By default, the thread is right-hand. For a left-hand thread, add the suffix -LH.Number of Starts: By default, all threads have a single start. Thus, the lead equals the pitch. For a multiple-start thread, the lead is also indicated by the letter L. For example, 1/4– 0.0625P – 0.1875L-ACMEdenotes a 0.25″ ACME thread with 3 starts. (0.1875/0.0625=3)Designation Examples of Acme ThreadsDesignationSeriesNominalDiameterTPIPitchLeadClassNumber of StartsThread Direction1/2-10-ACME 2GG0.5"100.1"=Pitch21Right Hand0.5-10-ACME 4CC0.5"100.1"=Pitch41Right Hand1/4– 0.0625P – 0.1875L-ACME 2GG0.25"160.0625"0.1875"23Right Hand2.5-3-ACME 4C-LHC2.5"30.3333"=Pitch41Left HandACME Threads – Basic DimensionsThe basic dimensions are nominal dimensions of the ACME profile without allowances and tolerances (The series and class define that – see below). They are based on standard ASTM B1.5. The basic dimensions can be used for design. However, for manufacturing and machining, you need the allowable range of each dimension. This data can be found in the ASTM standard or in the Limits and Dimensions section below. All the basic dimensions are derived from simple formulas based on the thread’s nominal diameter and pitch.SymbolsList of symbols used in charts and formulas of ACME ThreadsSymbolExplanationBasic Parameters - Diameters and PitchDMajor (Basic) diameter of internal threadD1Minor diameter of internal threadD2Pitch diameter of internal threaddExternal Major Diameterd1Minor diameter of external threadd2Pitch diameter of external threadnNumber of threds per Inch (TPI)PPitch (Distance)LLeadSNumber of StartshThread HeightFFlat WidthLELength of EngagmentαThread V half AngleAllowance, Deviation, and TolerancesTDTolerance - Minor diameter of internal thread & (Major Diameter)TD2Tolerance - Pitch diameter of internal threadTdTolerance - Minor diameter of external thread & (Major Diameter)Td2Tolerance - Minor diameter of external threadesAllowance - Pitch DiameterELAllowance - Major Diameter & (Minor Diameter)FormulasExternal Thread\( \begin{array}{l} \large d= \text{Diameter from designation} \\ \large n = \text{TPI from designation} \\ \large P = \frac{n}{TPI} \\ \large h = \frac{P}{2} \\ \large d _2= d\,-\,h \\ \large d_1 = d\,-\,P \\ \large F = 0.3707 \times P \\ \large 2\times\alpha = 29^{\circ} \\ \large \lambda = \tan^{-1} \left ( \frac{P \times S}{\pi \times d_2} \right ) \end{array} \)Internal thread\( \begin{array}{l} \large D= \text{Diameter from designation} \\ \large n = \text{TPI from designation} \\ \large P = \frac{n}{TPI} \\ \large h = \frac{P}{2} \\ \large D _2= D\,-\,h \\ \large D_1 = D\,-\,P \\ \large F = 0.3707 \times P \\ \large 2\times\alpha = 29^{\circ} \\ \large \lambda = \tan^{-1} \left ( \frac{P \times S}{\pi \times D_2} \right ) \end{array} \)Dimensions ChartClick the Thread Link to get the Full Thread Data for all classes in Inch and Metric units* Click icon to show Additional columns.(*) All dimensions are in InchesThreadMajor DiameterTPIPitchPitch DiameterMinor DiameterThread HeightFlat WidthLead AngleTap Drill Siuze1/4 - 16 ACME0.25160.06250.21880.18750.031250.02325.2°0.1875Metric Data ➢Tolerances ➢5/16 - 14 ACME0.3125140.07140.27680.24110.035710.02654.7°0.2411Metric Data ➢Tolerances ➢3/8 - 12 ACME0.375120.08330.33330.29170.041670.03094.55°0.2917Metric Data ➢Tolerances ➢7/16 - 12 ACME0.4375120.08330.39580.35420.041670.03093.83°0.3542Metric Data ➢Tolerances ➢1/2 - 10 ACME0.5100.10.450.40.050.03714.05°0.4Metric Data ➢Tolerances ➢5/8 - 8 ACME0.62580.1250.56250.50.06250.04634.05°0.5Metric Data ➢Tolerances ➢3/4 - 6 ACME0.7560.16670.66670.58330.083330.06184.55°0.5833Metric Data ➢Tolerances ➢7/8 - 6 ACME0.87560.16670.79170.70830.083330.06183.83°0.7083Metric Data ➢Tolerances ➢1 - 5 ACME150.20.90.80.10.07414.05°0.8Metric Data ➢Tolerances ➢1 1/8 - 5 ACME1.12550.21.0250.9250.10.07413.55°N/AMetric Data ➢Tolerances ➢1 1/4 - 5 ACME1.2550.21.151.050.10.07413.17°N/AMetric Data ➢Tolerances ➢1 3/8 - 4 ACME1.37540.251.251.1250.1250.09273.64°N/AMetric Data ➢Tolerances ➢1 1/2 - 4 ACME1.540.251.3751.250.1250.09273.31°N/AMetric Data ➢Tolerances ➢1 3/4 - 4 ACME1.7540.251.6251.50.1250.09272.8°N/AMetric Data ➢Tolerances ➢2 - 4 ACME240.251.8751.750.1250.09272.43°N/AMetric Data ➢Tolerances ➢2 1/4 - 3 ACME2.2530.33332.08331.91670.166670.12362.92°N/AMetric Data ➢Tolerances ➢2 1/2 - 3 ACME2.530.33332.33332.16670.166670.12362.6°N/AMetric Data ➢Tolerances ➢2 3/4 - 3 ACME2.7530.33332.58332.41670.166670.12362.35°N/AMetric Data ➢Tolerances ➢3 - 2 ACME320.52.752.50.250.18543.31°N/AMetric Data ➢Tolerances ➢3 1/2 - 2 ACME3.520.53.2530.250.18542.8°N/AMetric Data ➢Tolerances ➢4 - 2 ACME420.53.753.50.250.18542.43°N/AMetric Data ➢Tolerances ➢4 1/2 - 2 ACME4.520.54.2540.250.18542.14°N/AMetric Data ➢Tolerances ➢5 - 2 ACME520.54.754.50.250.18541.92°N/AMetric Data ➢Tolerances ➢ACME Threads – Limits of DimensionsTo manufacture or measure a thread, one has to know the maximum and minimum permissible values of the basic dimensions. These values are calculated according to the thread series and class (See below).Definition of terms:Allowance (Deviation): The minimum permissible distance between the basic and actual profile.Tolerance: The width of the tolerance field of a diameter on the actual thread profile. (Pitch, Major & Minor diameters)A small allowance means that the assembly of a male and female thread will be harder, but after assembly, there will be less freedom of movement.A large allowance means that the assembly of a male and female thread will be easier, but after assembly, there will be more freedom of movement.The allowance size does not influence a thread’s production difficulty or price.A wide tolerance is easier and cheaper to produce but yields a larger spread between threads.A narrow tolerance is challenging to produce and more expensive but yields a smaller spread between threads.Series & ClassesACME threads are divided into 3 series:G (General Purpose) – The most commonly used Acme threads. Wedging can occur under loads; therefore, it is recommended for applications where the screw and nut are supported individually.It has 3 precision classes 2G, 3G, and 4G.C (Centralized) – Tighter clearance between the internal and external threads. That prevents wedging on the flanks. More suitable for applications with higher load.It shares the exact basic dimensions of the C series. The difference is only in the tolerances.It has 3 precision classes 2C, 3C, and 4C.Stub – Compact threads with a 43% shorter stub height than standard Acme.Short and truncated thread profile, suitable for applications with limited space. Unlike G & C series, it only has a single precision class. They are defined in a separate ASTM document number B1.8.Series G & C have 3 preciosn classes:2G/2C – Least accurate and more commonly used.3G/3C – Medium accuracy.4G/4C – Highest accuracy, recommended to reduce backlash.Limits CalculationsASTM B1.5 defines how to calculate the tolerance of the following parameters:Major diameter (d / D)Minor diameter (d1 / D1)Pitch diameter (d2 / D2)Pitch & Lead (P / L)Angles between flanks (α)The below formulas are not valid for the following cases:Centralizes Acme series.Engagement lengths that are larger than twice the major diameter.Threads with multiple starts.TPI values that are not one of 2-6, 8, 10, 12, 14, or 16.Nominal diameters that are not one of 1/4, 5/16, 3/8, 7/16, 1/2, 3/4, 7/8, 1, 1-1/8, 1-1/4, 1-3/8, 1-1/2, 1-3/4, 2, 2-1/2, 2-3/4, 3, 3-1/2, 4, 4-1/2, or 5 Inches.For these cases, read the small print in ASTM B1.5 or use our Acme Thread Calculator  that handles all cases!Before calculating the limits, you need to obtain the following data:Allowance for major and minor diameters (el): Equals 0.002 for pitches of 10 TPI or coarser. For finer pitches, use 0.001.Allowance for pitch diameters (es): Should be obtained from ASM B1.5 (table 9). It cannot be calculated by a formula. You can either obtain it from the standard or use our below calculator.Payment options Pitch diameter tolerance (TD2): Should be obtained from ASM B1.5 (tables 5-7) or calculated with the below formula.\( TD_2 = K_P \times \sqrt{P} + K_D \times \sqrt{D} \)ClassKpKd2G / 3C0.030.0063G / 3C0.0140.00284G / 4C0.010.002Major diameter tolerance (Td): Equals to the TPI divided by 20. (But if less than 0.005, 0.005 should be used).After the above data has been obtained, you can proceed with the below formulas to calculate the limits. The below formulas are valid for all cases (Including The limitation listed above).Formulas for Limits of External Acme Thread\( \begin{array}{l} \large d_{max} = d_{nom} \\ \large d_{min} = d_{max}\,-\,T_d \\ \large d_{2\,max} = d_{2\,nom}\,-\,es \\ \large d_{2\,min} = d_{2\,max}\,-\,T_{d2} \\ \large d_{1\,max} = d_{1\,nom}\,-\,el \\ \large d_{1\,min} = d_{1\,max}\,-\,1.5 \times T_{d2} \end{array} \)Formulas for Limits of an Internal Acme Thread\( \begin{array}{l} \large D_{min} = D_{nom}\,+\,el \\ \large D_{max} = D_{min}\,+\,el \\ \large D_{2\,min} = D_{2\,nom} \\ \large D_{2\,max} = D_{2\,min}\,+\,T_{d2} \\ \large D_{1\,min} = D_{1\,nom} \\ \large D_{1\,max} = D_{1\,min}\,+\,T_{d} \end{array} \)Special ACME ThreadsBecause of the nature of its use cases and the limited list of standard configurations, special Acme threads are commonly used.What is considered a special Acme thread?A Diameter-Pitch combination that does not appear in this list.Multiple-Start threads.An engagement length that is larger than twice the major diameter.The Acme Thread Calculator  handles also Special Threads!Diameter-Pitch combinationsThe standard list of Acme threads in ASTM B1.5 has only one pitch option per diameter. However, “playing” with the pitch is an important design consideration since it allows us to increase the traverse speed by using a coarser pitch or increasing the accuracy by choosing a finer one. When opting for a special thread, ASTM B1.5 provides each pitch with the minimum and maximum allowed diameters.Premisable Diamter-Pitch CombinationsFor s thread with an intermediate pitch value, use the diameters shown for the next coarser pitch in the graph.To get the dimensions for such a thread, follow the formulas provided above or our Acme Thread Calculator, which knows how to handle any diameter-pitch combination.Multiple Start ThreadsMultiple-Start Acme threads are popular since they can bump up the traverse speed in multiples of 2, 3, 4, or more.The dimensions given in the standard are valid only for single-start threads. Use the below procedure to adjust the limits according to the number of starts.External threads (Screws) are not affected. The data for single-start threads should be used.For internal threads (Nuts), the allowance for major, minor, and pitch diameters is increased (relative to an equivalent single-start thread) by K x es. K depends on the number of starts: for 2 starts k=0.5, 3 starts k=0.75, and for 4 starts or more, k=1. Our Acme Thread Calculator also handles multiple-start threads!Length of EngagementIncreasing the length of the engagement means using a lengthier nut that can support higher forces. The data listed in ASTM B1.5 and the formulas given above are valid for engagement lengths up to twice the major diameter. The pitch diameter allowance (es) should be increased by 0.1 x es x (LE -  2 x d) when LE>2XD. Our Acme Thread Calculator also handles all engagement lengths.Related Glossary Terms:Lead (Threading)CNC MachineMajor DiameterTooth per inch (tpi)Thread Allowance (es)Minor DiameterPitch DiameterPitchThread Height (Depth)Tap Drill Size

Acme is a trapezoidal thread profile with a 29° V angle, defined in ASTM B1.5. It is the most popular thread used for traversing linear motion (For example, lead screws and power screws) due to its ability to withstand large loads and ease of manufacturing. It is found in industrial equipment such as CNC machines and conveyors, as well as everyday-life equipment such as a jack, which we use to replace a flat tire.Acme threads were first developed in the late 1800s by the American industrialist inventor William Sellers. Sellers aimed to create a leadscrew thread design that was stronger and easier to manufacture than the square thread design commonly used at the time. The resulting trapezoidal thread form became known as the Acme thread and quickly gained popularity in the design of lead screws and power screws.ACME – Table of ContentDesignationBasic DimensionsSymbolsFormulasDimensions ChartLimits of DimensionsSeries & ClassesLimits CalculationsSpecial ACME ThreadsDiameter-Pitch combinationsMultiple Start ThreadsLength of EngagementEasly obtain all the dimensions and tolerances with our Acme Thread Calculator DesignationBasic designation syntax:Nominal Diameter in Inch FractionPitch in TPISeries: G – General / C – CentralizedClass: 2, 3, or 4. Indicates the precision.Diameter:The diameter can range between 1/4″ to 5″.It is also allowed to denote the diameters with a decimal value. For example, 0.250 (1/4″), 0.4375 (7/16″), etc.Pitch:By default, the pitch is given in TPI. For example, 1/4-20 means a thread with a pitch of 20 TPI (1/20=0.05″).On multiple starts threads (see below), the pitch is indicated by distance. For example, 1/4-0.05P means a thread with a pitch of 0.05″ (same as 20 TPI).Series:G – General use.C – Centralized. This class defines a more restricted clearance at the major diameter of both the internal and external screws that prevent wedging on the flanks.Class:The class is defined by a number between 2 and 4.2– Lower precision.4 – Higher precision.Internal and external designations are exactly the same. You cannot tell from the description alone if the thread is external or internal.Additional Parameters:Direction: By default, the thread is right-hand. For a left-hand thread, add the suffix -LH.Number of Starts: By default, all threads have a single start. Thus, the lead equals the pitch. For a multiple-start thread, the lead is also indicated by the letter L. For example, 1/4– 0.0625P – 0.1875L-ACMEdenotes a 0.25″ ACME thread with 3 starts. (0.1875/0.0625=3)Designation Examples of Acme ThreadsDesignationSeriesNominalDiameterTPIPitchLeadClassNumber of StartsThread Direction1/2-10-ACME 2GG0.5"100.1"=Pitch21Right Hand0.5-10-ACME 4CC0.5"100.1"=Pitch41Right Hand1/4– 0.0625P – 0.1875L-ACME 2GG0.25"160.0625"0.1875"23Right Hand2.5-3-ACME 4C-LHC2.5"30.3333"=Pitch41Left HandACME Threads – Basic DimensionsThe basic dimensions are nominal dimensions of the ACME profile without allowances and tolerances (The series and class define that – see below). They are based on standard ASTM B1.5. The basic dimensions can be used for design. However, for manufacturing and machining, you need the allowable range of each dimension. This data can be found in the ASTM standard or in the Limits and Dimensions section below. All the basic dimensions are derived from simple formulas based on the thread’s nominal diameter and pitch.SymbolsList of symbols used in charts and formulas of ACME ThreadsSymbolExplanationBasic Parameters - Diameters and PitchDMajor (Basic) diameter of internal threadD1Minor diameter of internal threadD2Pitch diameter of internal threaddExternal Major Diameterd1Minor diameter of external threadd2Pitch diameter of external threadnNumber of threds per Inch (TPI)PPitch (Distance)LLeadSNumber of StartshThread HeightFFlat WidthLELength of EngagmentαThread V half AngleAllowance, Deviation, and TolerancesTDTolerance - Minor diameter of internal thread & (Major Diameter)TD2Tolerance - Pitch diameter of internal threadTdTolerance - Minor diameter of external thread & (Major Diameter)Td2Tolerance - Minor diameter of external threadesAllowance - Pitch DiameterELAllowance - Major Diameter & (Minor Diameter)FormulasExternal Thread\( \begin{array}{l} \large d= \text{Diameter from designation} \\ \large n = \text{TPI from designation} \\ \large P = \frac{n}{TPI} \\ \large h = \frac{P}{2} \\ \large d _2= d\,-\,h \\ \large d_1 = d\,-\,P \\ \large F = 0.3707 \times P \\ \large 2\times\alpha = 29^{\circ} \\ \large \lambda = \tan^{-1} \left ( \frac{P \times S}{\pi \times d_2} \right ) \end{array} \)Internal thread\( \begin{array}{l} \large D= \text{Diameter from designation} \\ \large n = \text{TPI from designation} \\ \large P = \frac{n}{TPI} \\ \large h = \frac{P}{2} \\ \large D _2= D\,-\,h \\ \large D_1 = D\,-\,P \\ \large F = 0.3707 \times P \\ \large 2\times\alpha = 29^{\circ} \\ \large \lambda = \tan^{-1} \left ( \frac{P \times S}{\pi \times D_2} \right ) \end{array} \)Dimensions ChartClick the Thread Link to get the Full Thread Data for all classes in Inch and Metric units* Click icon to show Additional columns.(*) All dimensions are in InchesThreadMajor DiameterTPIPitchPitch DiameterMinor DiameterThread HeightFlat WidthLead AngleTap Drill Siuze1/4 - 16 ACME0.25160.06250.21880.18750.031250.02325.2°0.1875Metric Data ➢Tolerances ➢5/16 - 14 ACME0.3125140.07140.27680.24110.035710.02654.7°0.2411Metric Data ➢Tolerances ➢3/8 - 12 ACME0.375120.08330.33330.29170.041670.03094.55°0.2917Metric Data ➢Tolerances ➢7/16 - 12 ACME0.4375120.08330.39580.35420.041670.03093.83°0.3542Metric Data ➢Tolerances ➢1/2 - 10 ACME0.5100.10.450.40.050.03714.05°0.4Metric Data ➢Tolerances ➢5/8 - 8 ACME0.62580.1250.56250.50.06250.04634.05°0.5Metric Data ➢Tolerances ➢3/4 - 6 ACME0.7560.16670.66670.58330.083330.06184.55°0.5833Metric Data ➢Tolerances ➢7/8 - 6 ACME0.87560.16670.79170.70830.083330.06183.83°0.7083Metric Data ➢Tolerances ➢1 - 5 ACME150.20.90.80.10.07414.05°0.8Metric Data ➢Tolerances ➢1 1/8 - 5 ACME1.12550.21.0250.9250.10.07413.55°N/AMetric Data ➢Tolerances ➢1 1/4 - 5 ACME1.2550.21.151.050.10.07413.17°N/AMetric Data ➢Tolerances ➢1 3/8 - 4 ACME1.37540.251.251.1250.1250.09273.64°N/AMetric Data ➢Tolerances ➢1 1/2 - 4 ACME1.540.251.3751.250.1250.09273.31°N/AMetric Data ➢Tolerances ➢1 3/4 - 4 ACME1.7540.251.6251.50.1250.09272.8°N/AMetric Data ➢Tolerances ➢2 - 4 ACME240.251.8751.750.1250.09272.43°N/AMetric Data ➢Tolerances ➢2 1/4 - 3 ACME2.2530.33332.08331.91670.166670.12362.92°N/AMetric Data ➢Tolerances ➢2 1/2 - 3 ACME2.530.33332.33332.16670.166670.12362.6°N/AMetric Data ➢Tolerances ➢2 3/4 - 3 ACME2.7530.33332.58332.41670.166670.12362.35°N/AMetric Data ➢Tolerances ➢3 - 2 ACME320.52.752.50.250.18543.31°N/AMetric Data ➢Tolerances ➢3 1/2 - 2 ACME3.520.53.2530.250.18542.8°N/AMetric Data ➢Tolerances ➢4 - 2 ACME420.53.753.50.250.18542.43°N/AMetric Data ➢Tolerances ➢4 1/2 - 2 ACME4.520.54.2540.250.18542.14°N/AMetric Data ➢Tolerances ➢5 - 2 ACME520.54.754.50.250.18541.92°N/AMetric Data ➢Tolerances ➢ACME Threads – Limits of DimensionsTo manufacture or measure a thread, one has to know the maximum and minimum permissible values of the basic dimensions. These values are calculated according to the thread series and class (See below).Definition of terms:Allowance (Deviation): The minimum permissible distance between the basic and actual profile.Tolerance: The width of the tolerance field of a diameter on the actual thread profile. (Pitch, Major & Minor diameters)A small allowance means that the assembly of a male and female thread will be harder, but after assembly, there will be less freedom of movement.A large allowance means that the assembly of a male and female thread will be easier, but after assembly, there will be more freedom of movement.The allowance size does not influence a thread’s production difficulty or price.A wide tolerance is easier and cheaper to produce but yields a larger spread between threads.A narrow tolerance is challenging to produce and more expensive but yields a smaller spread between threads.Series & ClassesACME threads are divided into 3 series:G (General Purpose) – The most commonly used Acme threads. Wedging can occur under loads; therefore, it is recommended for applications where the screw and nut are supported individually.It has 3 precision classes 2G, 3G, and 4G.C (Centralized) – Tighter clearance between the internal and external threads. That prevents wedging on the flanks. More suitable for applications with higher load.It shares the exact basic dimensions of the C series. The difference is only in the tolerances.It has 3 precision classes 2C, 3C, and 4C.Stub – Compact threads with a 43% shorter stub height than standard Acme.Short and truncated thread profile, suitable for applications with limited space. Unlike G & C series, it only has a single precision class. They are defined in a separate ASTM document number B1.8.Series G & C have 3 preciosn classes:2G/2C – Least accurate and more commonly used.3G/3C – Medium accuracy.4G/4C – Highest accuracy, recommended to reduce backlash.Limits CalculationsASTM B1.5 defines how to calculate the tolerance of the following parameters:Major diameter (d / D)Minor diameter (d1 / D1)Pitch diameter (d2 / D2)Pitch & Lead (P / L)Angles between flanks (α)The below formulas are not valid for the following cases:Centralizes Acme series.Engagement lengths that are larger than twice the major diameter.Threads with multiple starts.TPI values that are not one of 2-6, 8, 10, 12, 14, or 16.Nominal diameters that are not one of 1/4, 5/16, 3/8, 7/16, 1/2, 3/4, 7/8, 1, 1-1/8, 1-1/4, 1-3/8, 1-1/2, 1-3/4, 2, 2-1/2, 2-3/4, 3, 3-1/2, 4, 4-1/2, or 5 Inches.For these cases, read the small print in ASTM B1.5 or use our Acme Thread Calculator  that handles all cases!Before calculating the limits, you need to obtain the following data:Allowance for major and minor diameters (el): Equals 0.002 for pitches of 10 TPI or coarser. For finer pitches, use 0.001.Allowance for pitch diameters (es): Should be obtained from ASM B1.5 (table 9). It cannot be calculated by a formula. You can either obtain it from the standard or use our below calculator.Payment options Pitch diameter tolerance (TD2): Should be obtained from ASM B1.5 (tables 5-7) or calculated with the below formula.\( TD_2 = K_P \times \sqrt{P} + K_D \times \sqrt{D} \)ClassKpKd2G / 3C0.030.0063G / 3C0.0140.00284G / 4C0.010.002Major diameter tolerance (Td): Equals to the TPI divided by 20. (But if less than 0.005, 0.005 should be used).After the above data has been obtained, you can proceed with the below formulas to calculate the limits. The below formulas are valid for all cases (Including The limitation listed above).Formulas for Limits of External Acme Thread\( \begin{array}{l} \large d_{max} = d_{nom} \\ \large d_{min} = d_{max}\,-\,T_d \\ \large d_{2\,max} = d_{2\,nom}\,-\,es \\ \large d_{2\,min} = d_{2\,max}\,-\,T_{d2} \\ \large d_{1\,max} = d_{1\,nom}\,-\,el \\ \large d_{1\,min} = d_{1\,max}\,-\,1.5 \times T_{d2} \end{array} \)Formulas for Limits of an Internal Acme Thread\( \begin{array}{l} \large D_{min} = D_{nom}\,+\,el \\ \large D_{max} = D_{min}\,+\,el \\ \large D_{2\,min} = D_{2\,nom} \\ \large D_{2\,max} = D_{2\,min}\,+\,T_{d2} \\ \large D_{1\,min} = D_{1\,nom} \\ \large D_{1\,max} = D_{1\,min}\,+\,T_{d} \end{array} \)Special ACME ThreadsBecause of the nature of its use cases and the limited list of standard configurations, special Acme threads are commonly used.What is considered a special Acme thread?A Diameter-Pitch combination that does not appear in this list.Multiple-Start threads.An engagement length that is larger than twice the major diameter.The Acme Thread Calculator  handles also Special Threads!Diameter-Pitch combinationsThe standard list of Acme threads in ASTM B1.5 has only one pitch option per diameter. However, “playing” with the pitch is an important design consideration since it allows us to increase the traverse speed by using a coarser pitch or increasing the accuracy by choosing a finer one. When opting for a special thread, ASTM B1.5 provides each pitch with the minimum and maximum allowed diameters.Premisable Diamter-Pitch CombinationsFor s thread with an intermediate pitch value, use the diameters shown for the next coarser pitch in the graph.To get the dimensions for such a thread, follow the formulas provided above or our Acme Thread Calculator, which knows how to handle any diameter-pitch combination.Multiple Start ThreadsMultiple-Start Acme threads are popular since they can bump up the traverse speed in multiples of 2, 3, 4, or more.The dimensions given in the standard are valid only for single-start threads. Use the below procedure to adjust the limits according to the number of starts.External threads (Screws) are not affected. The data for single-start threads should be used.For internal threads (Nuts), the allowance for major, minor, and pitch diameters is increased (relative to an equivalent single-start thread) by K x es. K depends on the number of starts: for 2 starts k=0.5, 3 starts k=0.75, and for 4 starts or more, k=1. Our Acme Thread Calculator also handles multiple-start threads!Length of EngagementIncreasing the length of the engagement means using a lengthier nut that can support higher forces. The data listed in ASTM B1.5 and the formulas given above are valid for engagement lengths up to twice the major diameter. The pitch diameter allowance (es) should be increased by 0.1 x es x (LE -  2 x d) when LE>2XD. Our Acme Thread Calculator also handles all engagement lengths.Related Glossary Terms:Lead (Threading)CNC MachineMajor DiameterTooth per inch (tpi)Thread Allowance (es)Minor DiameterPitch DiameterPitchThread Height (Depth)Tap Drill Size

ACME threads are divided into 3 series:G (General Purpose) – The most commonly used Acme threads. Wedging can occur under loads; therefore, it is recommended for applications where the screw and nut are supported individually.It has 3 precision classes 2G, 3G, and 4G.C (Centralized) – Tighter clearance between the internal and external threads. That prevents wedging on the flanks. More suitable for applications with higher load.It shares the exact basic dimensions of the C series. The difference is only in the tolerances.It has 3 precision classes 2C, 3C, and 4C.Stub – Compact threads with a 43% shorter stub height than standard Acme.Short and truncated thread profile, suitable for applications with limited space. Unlike G & C series, it only has a single precision class. They are defined in a separate ASTM document number B1.8.Series G & C have 3 preciosn classes:2G/2C – Least accurate and more commonly used.3G/3C – Medium accuracy.4G/4C – Highest accuracy, recommended to reduce backlash.Limits CalculationsASTM B1.5 defines how to calculate the tolerance of the following parameters:Major diameter (d / D)Minor diameter (d1 / D1)Pitch diameter (d2 / D2)Pitch & Lead (P / L)Angles between flanks (α)The below formulas are not valid for the following cases:Centralizes Acme series.Engagement lengths that are larger than twice the major diameter.Threads with multiple starts.TPI values that are not one of 2-6, 8, 10, 12, 14, or 16.Nominal diameters that are not one of 1/4, 5/16, 3/8, 7/16, 1/2, 3/4, 7/8, 1, 1-1/8, 1-1/4, 1-3/8, 1-1/2, 1-3/4, 2, 2-1/2, 2-3/4, 3, 3-1/2, 4, 4-1/2, or 5 Inches.For these cases, read the small print in ASTM B1.5 or use our Acme Thread Calculator  that handles all cases!Before calculating the limits, you need to obtain the following data:Allowance for major and minor diameters (el): Equals 0.002 for pitches of 10 TPI or coarser. For finer pitches, use 0.001.Allowance for pitch diameters (es): Should be obtained from ASM B1.5 (table 9). It cannot be calculated by a formula. You can either obtain it from the standard or use our below calculator.Payment options Pitch diameter tolerance (TD2): Should be obtained from ASM B1.5 (tables 5-7) or calculated with the below formula.\( TD_2 = K_P \times \sqrt{P} + K_D \times \sqrt{D} \)ClassKpKd2G / 3C0.030.0063G / 3C0.0140.00284G / 4C0.010.002Major diameter tolerance (Td): Equals to the TPI divided by 20. (But if less than 0.005, 0.005 should be used).After the above data has been obtained, you can proceed with the below formulas to calculate the limits. The below formulas are valid for all cases (Including The limitation listed above).Formulas for Limits of External Acme Thread\( \begin{array}{l} \large d_{max} = d_{nom} \\ \large d_{min} = d_{max}\,-\,T_d \\ \large d_{2\,max} = d_{2\,nom}\,-\,es \\ \large d_{2\,min} = d_{2\,max}\,-\,T_{d2} \\ \large d_{1\,max} = d_{1\,nom}\,-\,el \\ \large d_{1\,min} = d_{1\,max}\,-\,1.5 \times T_{d2} \end{array} \)Formulas for Limits of an Internal Acme Thread\( \begin{array}{l} \large D_{min} = D_{nom}\,+\,el \\ \large D_{max} = D_{min}\,+\,el \\ \large D_{2\,min} = D_{2\,nom} \\ \large D_{2\,max} = D_{2\,min}\,+\,T_{d2} \\ \large D_{1\,min} = D_{1\,nom} \\ \large D_{1\,max} = D_{1\,min}\,+\,T_{d} \end{array} \)Special ACME ThreadsBecause of the nature of its use cases and the limited list of standard configurations, special Acme threads are commonly used.What is considered a special Acme thread?A Diameter-Pitch combination that does not appear in this list.Multiple-Start threads.An engagement length that is larger than twice the major diameter.The Acme Thread Calculator  handles also Special Threads!Diameter-Pitch combinationsThe standard list of Acme threads in ASTM B1.5 has only one pitch option per diameter. However, “playing” with the pitch is an important design consideration since it allows us to increase the traverse speed by using a coarser pitch or increasing the accuracy by choosing a finer one. When opting for a special thread, ASTM B1.5 provides each pitch with the minimum and maximum allowed diameters.Premisable Diamter-Pitch CombinationsFor s thread with an intermediate pitch value, use the diameters shown for the next coarser pitch in the graph.To get the dimensions for such a thread, follow the formulas provided above or our Acme Thread Calculator, which knows how to handle any diameter-pitch combination.Multiple Start ThreadsMultiple-Start Acme threads are popular since they can bump up the traverse speed in multiples of 2, 3, 4, or more.The dimensions given in the standard are valid only for single-start threads. Use the below procedure to adjust the limits according to the number of starts.External threads (Screws) are not affected. The data for single-start threads should be used.For internal threads (Nuts), the allowance for major, minor, and pitch diameters is increased (relative to an equivalent single-start thread) by K x es. K depends on the number of starts: for 2 starts k=0.5, 3 starts k=0.75, and for 4 starts or more, k=1. Our Acme Thread Calculator also handles multiple-start threads!Length of EngagementIncreasing the length of the engagement means using a lengthier nut that can support higher forces. The data listed in ASTM B1.5 and the formulas given above are valid for engagement lengths up to twice the major diameter. The pitch diameter allowance (es) should be increased by 0.1 x es x (LE -  2 x d) when LE>2XD. Our Acme Thread Calculator also handles all engagement lengths.Related Glossary Terms:Lead (Threading)CNC MachineMajor DiameterTooth per inch (tpi)Thread Allowance (es)Minor DiameterPitch DiameterPitchThread Height (Depth)Tap Drill Size

Click the Thread Link to get the Full Thread Data for all classes in Inch and Metric units* Click icon to show Additional columns.(*) All dimensions are in InchesThreadMajor DiameterTPIPitchPitch DiameterMinor DiameterThread HeightFlat WidthLead AngleTap Drill Siuze1/4 - 16 ACME0.25160.06250.21880.18750.031250.02325.2°0.1875Metric Data ➢Tolerances ➢5/16 - 14 ACME0.3125140.07140.27680.24110.035710.02654.7°0.2411Metric Data ➢Tolerances ➢3/8 - 12 ACME0.375120.08330.33330.29170.041670.03094.55°0.2917Metric Data ➢Tolerances ➢7/16 - 12 ACME0.4375120.08330.39580.35420.041670.03093.83°0.3542Metric Data ➢Tolerances ➢1/2 - 10 ACME0.5100.10.450.40.050.03714.05°0.4Metric Data ➢Tolerances ➢5/8 - 8 ACME0.62580.1250.56250.50.06250.04634.05°0.5Metric Data ➢Tolerances ➢3/4 - 6 ACME0.7560.16670.66670.58330.083330.06184.55°0.5833Metric Data ➢Tolerances ➢7/8 - 6 ACME0.87560.16670.79170.70830.083330.06183.83°0.7083Metric Data ➢Tolerances ➢1 - 5 ACME150.20.90.80.10.07414.05°0.8Metric Data ➢Tolerances ➢1 1/8 - 5 ACME1.12550.21.0250.9250.10.07413.55°N/AMetric Data ➢Tolerances ➢1 1/4 - 5 ACME1.2550.21.151.050.10.07413.17°N/AMetric Data ➢Tolerances ➢1 3/8 - 4 ACME1.37540.251.251.1250.1250.09273.64°N/AMetric Data ➢Tolerances ➢1 1/2 - 4 ACME1.540.251.3751.250.1250.09273.31°N/AMetric Data ➢Tolerances ➢1 3/4 - 4 ACME1.7540.251.6251.50.1250.09272.8°N/AMetric Data ➢Tolerances ➢2 - 4 ACME240.251.8751.750.1250.09272.43°N/AMetric Data ➢Tolerances ➢2 1/4 - 3 ACME2.2530.33332.08331.91670.166670.12362.92°N/AMetric Data ➢Tolerances ➢2 1/2 - 3 ACME2.530.33332.33332.16670.166670.12362.6°N/AMetric Data ➢Tolerances ➢2 3/4 - 3 ACME2.7530.33332.58332.41670.166670.12362.35°N/AMetric Data ➢Tolerances ➢3 - 2 ACME320.52.752.50.250.18543.31°N/AMetric Data ➢Tolerances ➢3 1/2 - 2 ACME3.520.53.2530.250.18542.8°N/AMetric Data ➢Tolerances ➢4 - 2 ACME420.53.753.50.250.18542.43°N/AMetric Data ➢Tolerances ➢4 1/2 - 2 ACME4.520.54.2540.250.18542.14°N/AMetric Data ➢Tolerances ➢5 - 2 ACME520.54.754.50.250.18541.92°N/AMetric Data ➢Tolerances ➢ACME Threads – Limits of DimensionsTo manufacture or measure a thread, one has to know the maximum and minimum permissible values of the basic dimensions. These values are calculated according to the thread series and class (See below).Definition of terms:Allowance (Deviation): The minimum permissible distance between the basic and actual profile.Tolerance: The width of the tolerance field of a diameter on the actual thread profile. (Pitch, Major & Minor diameters)A small allowance means that the assembly of a male and female thread will be harder, but after assembly, there will be less freedom of movement.A large allowance means that the assembly of a male and female thread will be easier, but after assembly, there will be more freedom of movement.The allowance size does not influence a thread’s production difficulty or price.A wide tolerance is easier and cheaper to produce but yields a larger spread between threads.A narrow tolerance is challenging to produce and more expensive but yields a smaller spread between threads.Series & ClassesACME threads are divided into 3 series:G (General Purpose) – The most commonly used Acme threads. Wedging can occur under loads; therefore, it is recommended for applications where the screw and nut are supported individually.It has 3 precision classes 2G, 3G, and 4G.C (Centralized) – Tighter clearance between the internal and external threads. That prevents wedging on the flanks. More suitable for applications with higher load.It shares the exact basic dimensions of the C series. The difference is only in the tolerances.It has 3 precision classes 2C, 3C, and 4C.Stub – Compact threads with a 43% shorter stub height than standard Acme.Short and truncated thread profile, suitable for applications with limited space. Unlike G & C series, it only has a single precision class. They are defined in a separate ASTM document number B1.8.Series G & C have 3 preciosn classes:2G/2C – Least accurate and more commonly used.3G/3C – Medium accuracy.4G/4C – Highest accuracy, recommended to reduce backlash.Limits CalculationsASTM B1.5 defines how to calculate the tolerance of the following parameters:Major diameter (d / D)Minor diameter (d1 / D1)Pitch diameter (d2 / D2)Pitch & Lead (P / L)Angles between flanks (α)The below formulas are not valid for the following cases:Centralizes Acme series.Engagement lengths that are larger than twice the major diameter.Threads with multiple starts.TPI values that are not one of 2-6, 8, 10, 12, 14, or 16.Nominal diameters that are not one of 1/4, 5/16, 3/8, 7/16, 1/2, 3/4, 7/8, 1, 1-1/8, 1-1/4, 1-3/8, 1-1/2, 1-3/4, 2, 2-1/2, 2-3/4, 3, 3-1/2, 4, 4-1/2, or 5 Inches.For these cases, read the small print in ASTM B1.5 or use our Acme Thread Calculator  that handles all cases!Before calculating the limits, you need to obtain the following data:Allowance for major and minor diameters (el): Equals 0.002 for pitches of 10 TPI or coarser. For finer pitches, use 0.001.Allowance for pitch diameters (es): Should be obtained from ASM B1.5 (table 9). It cannot be calculated by a formula. You can either obtain it from the standard or use our below calculator.Payment options Pitch diameter tolerance (TD2): Should be obtained from ASM B1.5 (tables 5-7) or calculated with the below formula.\( TD_2 = K_P \times \sqrt{P} + K_D \times \sqrt{D} \)ClassKpKd2G / 3C0.030.0063G / 3C0.0140.00284G / 4C0.010.002Major diameter tolerance (Td): Equals to the TPI divided by 20. (But if less than 0.005, 0.005 should be used).After the above data has been obtained, you can proceed with the below formulas to calculate the limits. The below formulas are valid for all cases (Including The limitation listed above).Formulas for Limits of External Acme Thread\( \begin{array}{l} \large d_{max} = d_{nom} \\ \large d_{min} = d_{max}\,-\,T_d \\ \large d_{2\,max} = d_{2\,nom}\,-\,es \\ \large d_{2\,min} = d_{2\,max}\,-\,T_{d2} \\ \large d_{1\,max} = d_{1\,nom}\,-\,el \\ \large d_{1\,min} = d_{1\,max}\,-\,1.5 \times T_{d2} \end{array} \)Formulas for Limits of an Internal Acme Thread\( \begin{array}{l} \large D_{min} = D_{nom}\,+\,el \\ \large D_{max} = D_{min}\,+\,el \\ \large D_{2\,min} = D_{2\,nom} \\ \large D_{2\,max} = D_{2\,min}\,+\,T_{d2} \\ \large D_{1\,min} = D_{1\,nom} \\ \large D_{1\,max} = D_{1\,min}\,+\,T_{d} \end{array} \)Special ACME ThreadsBecause of the nature of its use cases and the limited list of standard configurations, special Acme threads are commonly used.What is considered a special Acme thread?A Diameter-Pitch combination that does not appear in this list.Multiple-Start threads.An engagement length that is larger than twice the major diameter.The Acme Thread Calculator  handles also Special Threads!Diameter-Pitch combinationsThe standard list of Acme threads in ASTM B1.5 has only one pitch option per diameter. However, “playing” with the pitch is an important design consideration since it allows us to increase the traverse speed by using a coarser pitch or increasing the accuracy by choosing a finer one. When opting for a special thread, ASTM B1.5 provides each pitch with the minimum and maximum allowed diameters.Premisable Diamter-Pitch CombinationsFor s thread with an intermediate pitch value, use the diameters shown for the next coarser pitch in the graph.To get the dimensions for such a thread, follow the formulas provided above or our Acme Thread Calculator, which knows how to handle any diameter-pitch combination.Multiple Start ThreadsMultiple-Start Acme threads are popular since they can bump up the traverse speed in multiples of 2, 3, 4, or more.The dimensions given in the standard are valid only for single-start threads. Use the below procedure to adjust the limits according to the number of starts.External threads (Screws) are not affected. The data for single-start threads should be used.For internal threads (Nuts), the allowance for major, minor, and pitch diameters is increased (relative to an equivalent single-start thread) by K x es. K depends on the number of starts: for 2 starts k=0.5, 3 starts k=0.75, and for 4 starts or more, k=1. Our Acme Thread Calculator also handles multiple-start threads!Length of EngagementIncreasing the length of the engagement means using a lengthier nut that can support higher forces. The data listed in ASTM B1.5 and the formulas given above are valid for engagement lengths up to twice the major diameter. The pitch diameter allowance (es) should be increased by 0.1 x es x (LE -  2 x d) when LE>2XD. Our Acme Thread Calculator also handles all engagement lengths.Related Glossary Terms:Lead (Threading)CNC MachineMajor DiameterTooth per inch (tpi)Thread Allowance (es)Minor DiameterPitch DiameterPitchThread Height (Depth)Tap Drill Size

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An electrical power distribution system provides electric power to individual consumer premises. It includes distribution substations, primary distribution feeders, distribution transformers, distributors, and service mains.

Diameter:The diameter can range between 1/4″ to 5″.It is also allowed to denote the diameters with a decimal value. For example, 0.250 (1/4″), 0.4375 (7/16″), etc.Pitch:By default, the pitch is given in TPI. For example, 1/4-20 means a thread with a pitch of 20 TPI (1/20=0.05″).On multiple starts threads (see below), the pitch is indicated by distance. For example, 1/4-0.05P means a thread with a pitch of 0.05″ (same as 20 TPI).Series:G – General use.C – Centralized. This class defines a more restricted clearance at the major diameter of both the internal and external screws that prevent wedging on the flanks.Class:The class is defined by a number between 2 and 4.2– Lower precision.4 – Higher precision.Internal and external designations are exactly the same. You cannot tell from the description alone if the thread is external or internal.Additional Parameters:Direction: By default, the thread is right-hand. For a left-hand thread, add the suffix -LH.Number of Starts: By default, all threads have a single start. Thus, the lead equals the pitch. For a multiple-start thread, the lead is also indicated by the letter L. For example, 1/4– 0.0625P – 0.1875L-ACMEdenotes a 0.25″ ACME thread with 3 starts. (0.1875/0.0625=3)Designation Examples of Acme ThreadsDesignationSeriesNominalDiameterTPIPitchLeadClassNumber of StartsThread Direction1/2-10-ACME 2GG0.5"100.1"=Pitch21Right Hand0.5-10-ACME 4CC0.5"100.1"=Pitch41Right Hand1/4– 0.0625P – 0.1875L-ACME 2GG0.25"160.0625"0.1875"23Right Hand2.5-3-ACME 4C-LHC2.5"30.3333"=Pitch41Left HandACME Threads – Basic DimensionsThe basic dimensions are nominal dimensions of the ACME profile without allowances and tolerances (The series and class define that – see below). They are based on standard ASTM B1.5. The basic dimensions can be used for design. However, for manufacturing and machining, you need the allowable range of each dimension. This data can be found in the ASTM standard or in the Limits and Dimensions section below. All the basic dimensions are derived from simple formulas based on the thread’s nominal diameter and pitch.SymbolsList of symbols used in charts and formulas of ACME ThreadsSymbolExplanationBasic Parameters - Diameters and PitchDMajor (Basic) diameter of internal threadD1Minor diameter of internal threadD2Pitch diameter of internal threaddExternal Major Diameterd1Minor diameter of external threadd2Pitch diameter of external threadnNumber of threds per Inch (TPI)PPitch (Distance)LLeadSNumber of StartshThread HeightFFlat WidthLELength of EngagmentαThread V half AngleAllowance, Deviation, and TolerancesTDTolerance - Minor diameter of internal thread & (Major Diameter)TD2Tolerance - Pitch diameter of internal threadTdTolerance - Minor diameter of external thread & (Major Diameter)Td2Tolerance - Minor diameter of external threadesAllowance - Pitch DiameterELAllowance - Major Diameter & (Minor Diameter)FormulasExternal Thread\( \begin{array}{l} \large d= \text{Diameter from designation} \\ \large n = \text{TPI from designation} \\ \large P = \frac{n}{TPI} \\ \large h = \frac{P}{2} \\ \large d _2= d\,-\,h \\ \large d_1 = d\,-\,P \\ \large F = 0.3707 \times P \\ \large 2\times\alpha = 29^{\circ} \\ \large \lambda = \tan^{-1} \left ( \frac{P \times S}{\pi \times d_2} \right ) \end{array} \)Internal thread\( \begin{array}{l} \large D= \text{Diameter from designation} \\ \large n = \text{TPI from designation} \\ \large P = \frac{n}{TPI} \\ \large h = \frac{P}{2} \\ \large D _2= D\,-\,h \\ \large D_1 = D\,-\,P \\ \large F = 0.3707 \times P \\ \large 2\times\alpha = 29^{\circ} \\ \large \lambda = \tan^{-1} \left ( \frac{P \times S}{\pi \times D_2} \right ) \end{array} \)Dimensions ChartClick the Thread Link to get the Full Thread Data for all classes in Inch and Metric units* Click icon to show Additional columns.(*) All dimensions are in InchesThreadMajor DiameterTPIPitchPitch DiameterMinor DiameterThread HeightFlat WidthLead AngleTap Drill Siuze1/4 - 16 ACME0.25160.06250.21880.18750.031250.02325.2°0.1875Metric Data ➢Tolerances ➢5/16 - 14 ACME0.3125140.07140.27680.24110.035710.02654.7°0.2411Metric Data ➢Tolerances ➢3/8 - 12 ACME0.375120.08330.33330.29170.041670.03094.55°0.2917Metric Data ➢Tolerances ➢7/16 - 12 ACME0.4375120.08330.39580.35420.041670.03093.83°0.3542Metric Data ➢Tolerances ➢1/2 - 10 ACME0.5100.10.450.40.050.03714.05°0.4Metric Data ➢Tolerances ➢5/8 - 8 ACME0.62580.1250.56250.50.06250.04634.05°0.5Metric Data ➢Tolerances ➢3/4 - 6 ACME0.7560.16670.66670.58330.083330.06184.55°0.5833Metric Data ➢Tolerances ➢7/8 - 6 ACME0.87560.16670.79170.70830.083330.06183.83°0.7083Metric Data ➢Tolerances ➢1 - 5 ACME150.20.90.80.10.07414.05°0.8Metric Data ➢Tolerances ➢1 1/8 - 5 ACME1.12550.21.0250.9250.10.07413.55°N/AMetric Data ➢Tolerances ➢1 1/4 - 5 ACME1.2550.21.151.050.10.07413.17°N/AMetric Data ➢Tolerances ➢1 3/8 - 4 ACME1.37540.251.251.1250.1250.09273.64°N/AMetric Data ➢Tolerances ➢1 1/2 - 4 ACME1.540.251.3751.250.1250.09273.31°N/AMetric Data ➢Tolerances ➢1 3/4 - 4 ACME1.7540.251.6251.50.1250.09272.8°N/AMetric Data ➢Tolerances ➢2 - 4 ACME240.251.8751.750.1250.09272.43°N/AMetric Data ➢Tolerances ➢2 1/4 - 3 ACME2.2530.33332.08331.91670.166670.12362.92°N/AMetric Data ➢Tolerances ➢2 1/2 - 3 ACME2.530.33332.33332.16670.166670.12362.6°N/AMetric Data ➢Tolerances ➢2 3/4 - 3 ACME2.7530.33332.58332.41670.166670.12362.35°N/AMetric Data ➢Tolerances ➢3 - 2 ACME320.52.752.50.250.18543.31°N/AMetric Data ➢Tolerances ➢3 1/2 - 2 ACME3.520.53.2530.250.18542.8°N/AMetric Data ➢Tolerances ➢4 - 2 ACME420.53.753.50.250.18542.43°N/AMetric Data ➢Tolerances ➢4 1/2 - 2 ACME4.520.54.2540.250.18542.14°N/AMetric Data ➢Tolerances ➢5 - 2 ACME520.54.754.50.250.18541.92°N/AMetric Data ➢Tolerances ➢ACME Threads – Limits of DimensionsTo manufacture or measure a thread, one has to know the maximum and minimum permissible values of the basic dimensions. These values are calculated according to the thread series and class (See below).Definition of terms:Allowance (Deviation): The minimum permissible distance between the basic and actual profile.Tolerance: The width of the tolerance field of a diameter on the actual thread profile. (Pitch, Major & Minor diameters)A small allowance means that the assembly of a male and female thread will be harder, but after assembly, there will be less freedom of movement.A large allowance means that the assembly of a male and female thread will be easier, but after assembly, there will be more freedom of movement.The allowance size does not influence a thread’s production difficulty or price.A wide tolerance is easier and cheaper to produce but yields a larger spread between threads.A narrow tolerance is challenging to produce and more expensive but yields a smaller spread between threads.Series & ClassesACME threads are divided into 3 series:G (General Purpose) – The most commonly used Acme threads. Wedging can occur under loads; therefore, it is recommended for applications where the screw and nut are supported individually.It has 3 precision classes 2G, 3G, and 4G.C (Centralized) – Tighter clearance between the internal and external threads. That prevents wedging on the flanks. More suitable for applications with higher load.It shares the exact basic dimensions of the C series. The difference is only in the tolerances.It has 3 precision classes 2C, 3C, and 4C.Stub – Compact threads with a 43% shorter stub height than standard Acme.Short and truncated thread profile, suitable for applications with limited space. Unlike G & C series, it only has a single precision class. They are defined in a separate ASTM document number B1.8.Series G & C have 3 preciosn classes:2G/2C – Least accurate and more commonly used.3G/3C – Medium accuracy.4G/4C – Highest accuracy, recommended to reduce backlash.Limits CalculationsASTM B1.5 defines how to calculate the tolerance of the following parameters:Major diameter (d / D)Minor diameter (d1 / D1)Pitch diameter (d2 / D2)Pitch & Lead (P / L)Angles between flanks (α)The below formulas are not valid for the following cases:Centralizes Acme series.Engagement lengths that are larger than twice the major diameter.Threads with multiple starts.TPI values that are not one of 2-6, 8, 10, 12, 14, or 16.Nominal diameters that are not one of 1/4, 5/16, 3/8, 7/16, 1/2, 3/4, 7/8, 1, 1-1/8, 1-1/4, 1-3/8, 1-1/2, 1-3/4, 2, 2-1/2, 2-3/4, 3, 3-1/2, 4, 4-1/2, or 5 Inches.For these cases, read the small print in ASTM B1.5 or use our Acme Thread Calculator  that handles all cases!Before calculating the limits, you need to obtain the following data:Allowance for major and minor diameters (el): Equals 0.002 for pitches of 10 TPI or coarser. For finer pitches, use 0.001.Allowance for pitch diameters (es): Should be obtained from ASM B1.5 (table 9). It cannot be calculated by a formula. You can either obtain it from the standard or use our below calculator.Payment options Pitch diameter tolerance (TD2): Should be obtained from ASM B1.5 (tables 5-7) or calculated with the below formula.\( TD_2 = K_P \times \sqrt{P} + K_D \times \sqrt{D} \)ClassKpKd2G / 3C0.030.0063G / 3C0.0140.00284G / 4C0.010.002Major diameter tolerance (Td): Equals to the TPI divided by 20. (But if less than 0.005, 0.005 should be used).After the above data has been obtained, you can proceed with the below formulas to calculate the limits. The below formulas are valid for all cases (Including The limitation listed above).Formulas for Limits of External Acme Thread\( \begin{array}{l} \large d_{max} = d_{nom} \\ \large d_{min} = d_{max}\,-\,T_d \\ \large d_{2\,max} = d_{2\,nom}\,-\,es \\ \large d_{2\,min} = d_{2\,max}\,-\,T_{d2} \\ \large d_{1\,max} = d_{1\,nom}\,-\,el \\ \large d_{1\,min} = d_{1\,max}\,-\,1.5 \times T_{d2} \end{array} \)Formulas for Limits of an Internal Acme Thread\( \begin{array}{l} \large D_{min} = D_{nom}\,+\,el \\ \large D_{max} = D_{min}\,+\,el \\ \large D_{2\,min} = D_{2\,nom} \\ \large D_{2\,max} = D_{2\,min}\,+\,T_{d2} \\ \large D_{1\,min} = D_{1\,nom} \\ \large D_{1\,max} = D_{1\,min}\,+\,T_{d} \end{array} \)Special ACME ThreadsBecause of the nature of its use cases and the limited list of standard configurations, special Acme threads are commonly used.What is considered a special Acme thread?A Diameter-Pitch combination that does not appear in this list.Multiple-Start threads.An engagement length that is larger than twice the major diameter.The Acme Thread Calculator  handles also Special Threads!Diameter-Pitch combinationsThe standard list of Acme threads in ASTM B1.5 has only one pitch option per diameter. However, “playing” with the pitch is an important design consideration since it allows us to increase the traverse speed by using a coarser pitch or increasing the accuracy by choosing a finer one. When opting for a special thread, ASTM B1.5 provides each pitch with the minimum and maximum allowed diameters.Premisable Diamter-Pitch CombinationsFor s thread with an intermediate pitch value, use the diameters shown for the next coarser pitch in the graph.To get the dimensions for such a thread, follow the formulas provided above or our Acme Thread Calculator, which knows how to handle any diameter-pitch combination.Multiple Start ThreadsMultiple-Start Acme threads are popular since they can bump up the traverse speed in multiples of 2, 3, 4, or more.The dimensions given in the standard are valid only for single-start threads. Use the below procedure to adjust the limits according to the number of starts.External threads (Screws) are not affected. The data for single-start threads should be used.For internal threads (Nuts), the allowance for major, minor, and pitch diameters is increased (relative to an equivalent single-start thread) by K x es. K depends on the number of starts: for 2 starts k=0.5, 3 starts k=0.75, and for 4 starts or more, k=1. Our Acme Thread Calculator also handles multiple-start threads!Length of EngagementIncreasing the length of the engagement means using a lengthier nut that can support higher forces. The data listed in ASTM B1.5 and the formulas given above are valid for engagement lengths up to twice the major diameter. The pitch diameter allowance (es) should be increased by 0.1 x es x (LE -  2 x d) when LE>2XD. Our Acme Thread Calculator also handles all engagement lengths.Related Glossary Terms:Lead (Threading)CNC MachineMajor DiameterTooth per inch (tpi)Thread Allowance (es)Minor DiameterPitch DiameterPitchThread Height (Depth)Tap Drill Size

Acme threads were first developed in the late 1800s by the American industrialist inventor William Sellers. Sellers aimed to create a leadscrew thread design that was stronger and easier to manufacture than the square thread design commonly used at the time. The resulting trapezoidal thread form became known as the Acme thread and quickly gained popularity in the design of lead screws and power screws.ACME – Table of ContentDesignationBasic DimensionsSymbolsFormulasDimensions ChartLimits of DimensionsSeries & ClassesLimits CalculationsSpecial ACME ThreadsDiameter-Pitch combinationsMultiple Start ThreadsLength of EngagementEasly obtain all the dimensions and tolerances with our Acme Thread Calculator DesignationBasic designation syntax:Nominal Diameter in Inch FractionPitch in TPISeries: G – General / C – CentralizedClass: 2, 3, or 4. Indicates the precision.Diameter:The diameter can range between 1/4″ to 5″.It is also allowed to denote the diameters with a decimal value. For example, 0.250 (1/4″), 0.4375 (7/16″), etc.Pitch:By default, the pitch is given in TPI. For example, 1/4-20 means a thread with a pitch of 20 TPI (1/20=0.05″).On multiple starts threads (see below), the pitch is indicated by distance. For example, 1/4-0.05P means a thread with a pitch of 0.05″ (same as 20 TPI).Series:G – General use.C – Centralized. This class defines a more restricted clearance at the major diameter of both the internal and external screws that prevent wedging on the flanks.Class:The class is defined by a number between 2 and 4.2– Lower precision.4 – Higher precision.Internal and external designations are exactly the same. You cannot tell from the description alone if the thread is external or internal.Additional Parameters:Direction: By default, the thread is right-hand. For a left-hand thread, add the suffix -LH.Number of Starts: By default, all threads have a single start. Thus, the lead equals the pitch. For a multiple-start thread, the lead is also indicated by the letter L. For example, 1/4– 0.0625P – 0.1875L-ACMEdenotes a 0.25″ ACME thread with 3 starts. (0.1875/0.0625=3)Designation Examples of Acme ThreadsDesignationSeriesNominalDiameterTPIPitchLeadClassNumber of StartsThread Direction1/2-10-ACME 2GG0.5"100.1"=Pitch21Right Hand0.5-10-ACME 4CC0.5"100.1"=Pitch41Right Hand1/4– 0.0625P – 0.1875L-ACME 2GG0.25"160.0625"0.1875"23Right Hand2.5-3-ACME 4C-LHC2.5"30.3333"=Pitch41Left HandACME Threads – Basic DimensionsThe basic dimensions are nominal dimensions of the ACME profile without allowances and tolerances (The series and class define that – see below). They are based on standard ASTM B1.5. The basic dimensions can be used for design. However, for manufacturing and machining, you need the allowable range of each dimension. This data can be found in the ASTM standard or in the Limits and Dimensions section below. All the basic dimensions are derived from simple formulas based on the thread’s nominal diameter and pitch.SymbolsList of symbols used in charts and formulas of ACME ThreadsSymbolExplanationBasic Parameters - Diameters and PitchDMajor (Basic) diameter of internal threadD1Minor diameter of internal threadD2Pitch diameter of internal threaddExternal Major Diameterd1Minor diameter of external threadd2Pitch diameter of external threadnNumber of threds per Inch (TPI)PPitch (Distance)LLeadSNumber of StartshThread HeightFFlat WidthLELength of EngagmentαThread V half AngleAllowance, Deviation, and TolerancesTDTolerance - Minor diameter of internal thread & (Major Diameter)TD2Tolerance - Pitch diameter of internal threadTdTolerance - Minor diameter of external thread & (Major Diameter)Td2Tolerance - Minor diameter of external threadesAllowance - Pitch DiameterELAllowance - Major Diameter & (Minor Diameter)FormulasExternal Thread\( \begin{array}{l} \large d= \text{Diameter from designation} \\ \large n = \text{TPI from designation} \\ \large P = \frac{n}{TPI} \\ \large h = \frac{P}{2} \\ \large d _2= d\,-\,h \\ \large d_1 = d\,-\,P \\ \large F = 0.3707 \times P \\ \large 2\times\alpha = 29^{\circ} \\ \large \lambda = \tan^{-1} \left ( \frac{P \times S}{\pi \times d_2} \right ) \end{array} \)Internal thread\( \begin{array}{l} \large D= \text{Diameter from designation} \\ \large n = \text{TPI from designation} \\ \large P = \frac{n}{TPI} \\ \large h = \frac{P}{2} \\ \large D _2= D\,-\,h \\ \large D_1 = D\,-\,P \\ \large F = 0.3707 \times P \\ \large 2\times\alpha = 29^{\circ} \\ \large \lambda = \tan^{-1} \left ( \frac{P \times S}{\pi \times D_2} \right ) \end{array} \)Dimensions ChartClick the Thread Link to get the Full Thread Data for all classes in Inch and Metric units* Click icon to show Additional columns.(*) All dimensions are in InchesThreadMajor DiameterTPIPitchPitch DiameterMinor DiameterThread HeightFlat WidthLead AngleTap Drill Siuze1/4 - 16 ACME0.25160.06250.21880.18750.031250.02325.2°0.1875Metric Data ➢Tolerances ➢5/16 - 14 ACME0.3125140.07140.27680.24110.035710.02654.7°0.2411Metric Data ➢Tolerances ➢3/8 - 12 ACME0.375120.08330.33330.29170.041670.03094.55°0.2917Metric Data ➢Tolerances ➢7/16 - 12 ACME0.4375120.08330.39580.35420.041670.03093.83°0.3542Metric Data ➢Tolerances ➢1/2 - 10 ACME0.5100.10.450.40.050.03714.05°0.4Metric Data ➢Tolerances ➢5/8 - 8 ACME0.62580.1250.56250.50.06250.04634.05°0.5Metric Data ➢Tolerances ➢3/4 - 6 ACME0.7560.16670.66670.58330.083330.06184.55°0.5833Metric Data ➢Tolerances ➢7/8 - 6 ACME0.87560.16670.79170.70830.083330.06183.83°0.7083Metric Data ➢Tolerances ➢1 - 5 ACME150.20.90.80.10.07414.05°0.8Metric Data ➢Tolerances ➢1 1/8 - 5 ACME1.12550.21.0250.9250.10.07413.55°N/AMetric Data ➢Tolerances ➢1 1/4 - 5 ACME1.2550.21.151.050.10.07413.17°N/AMetric Data ➢Tolerances ➢1 3/8 - 4 ACME1.37540.251.251.1250.1250.09273.64°N/AMetric Data ➢Tolerances ➢1 1/2 - 4 ACME1.540.251.3751.250.1250.09273.31°N/AMetric Data ➢Tolerances ➢1 3/4 - 4 ACME1.7540.251.6251.50.1250.09272.8°N/AMetric Data ➢Tolerances ➢2 - 4 ACME240.251.8751.750.1250.09272.43°N/AMetric Data ➢Tolerances ➢2 1/4 - 3 ACME2.2530.33332.08331.91670.166670.12362.92°N/AMetric Data ➢Tolerances ➢2 1/2 - 3 ACME2.530.33332.33332.16670.166670.12362.6°N/AMetric Data ➢Tolerances ➢2 3/4 - 3 ACME2.7530.33332.58332.41670.166670.12362.35°N/AMetric Data ➢Tolerances ➢3 - 2 ACME320.52.752.50.250.18543.31°N/AMetric Data ➢Tolerances ➢3 1/2 - 2 ACME3.520.53.2530.250.18542.8°N/AMetric Data ➢Tolerances ➢4 - 2 ACME420.53.753.50.250.18542.43°N/AMetric Data ➢Tolerances ➢4 1/2 - 2 ACME4.520.54.2540.250.18542.14°N/AMetric Data ➢Tolerances ➢5 - 2 ACME520.54.754.50.250.18541.92°N/AMetric Data ➢Tolerances ➢ACME Threads – Limits of DimensionsTo manufacture or measure a thread, one has to know the maximum and minimum permissible values of the basic dimensions. These values are calculated according to the thread series and class (See below).Definition of terms:Allowance (Deviation): The minimum permissible distance between the basic and actual profile.Tolerance: The width of the tolerance field of a diameter on the actual thread profile. (Pitch, Major & Minor diameters)A small allowance means that the assembly of a male and female thread will be harder, but after assembly, there will be less freedom of movement.A large allowance means that the assembly of a male and female thread will be easier, but after assembly, there will be more freedom of movement.The allowance size does not influence a thread’s production difficulty or price.A wide tolerance is easier and cheaper to produce but yields a larger spread between threads.A narrow tolerance is challenging to produce and more expensive but yields a smaller spread between threads.Series & ClassesACME threads are divided into 3 series:G (General Purpose) – The most commonly used Acme threads. Wedging can occur under loads; therefore, it is recommended for applications where the screw and nut are supported individually.It has 3 precision classes 2G, 3G, and 4G.C (Centralized) – Tighter clearance between the internal and external threads. That prevents wedging on the flanks. More suitable for applications with higher load.It shares the exact basic dimensions of the C series. The difference is only in the tolerances.It has 3 precision classes 2C, 3C, and 4C.Stub – Compact threads with a 43% shorter stub height than standard Acme.Short and truncated thread profile, suitable for applications with limited space. Unlike G & C series, it only has a single precision class. They are defined in a separate ASTM document number B1.8.Series G & C have 3 preciosn classes:2G/2C – Least accurate and more commonly used.3G/3C – Medium accuracy.4G/4C – Highest accuracy, recommended to reduce backlash.Limits CalculationsASTM B1.5 defines how to calculate the tolerance of the following parameters:Major diameter (d / D)Minor diameter (d1 / D1)Pitch diameter (d2 / D2)Pitch & Lead (P / L)Angles between flanks (α)The below formulas are not valid for the following cases:Centralizes Acme series.Engagement lengths that are larger than twice the major diameter.Threads with multiple starts.TPI values that are not one of 2-6, 8, 10, 12, 14, or 16.Nominal diameters that are not one of 1/4, 5/16, 3/8, 7/16, 1/2, 3/4, 7/8, 1, 1-1/8, 1-1/4, 1-3/8, 1-1/2, 1-3/4, 2, 2-1/2, 2-3/4, 3, 3-1/2, 4, 4-1/2, or 5 Inches.For these cases, read the small print in ASTM B1.5 or use our Acme Thread Calculator  that handles all cases!Before calculating the limits, you need to obtain the following data:Allowance for major and minor diameters (el): Equals 0.002 for pitches of 10 TPI or coarser. For finer pitches, use 0.001.Allowance for pitch diameters (es): Should be obtained from ASM B1.5 (table 9). It cannot be calculated by a formula. You can either obtain it from the standard or use our below calculator.Payment options Pitch diameter tolerance (TD2): Should be obtained from ASM B1.5 (tables 5-7) or calculated with the below formula.\( TD_2 = K_P \times \sqrt{P} + K_D \times \sqrt{D} \)ClassKpKd2G / 3C0.030.0063G / 3C0.0140.00284G / 4C0.010.002Major diameter tolerance (Td): Equals to the TPI divided by 20. (But if less than 0.005, 0.005 should be used).After the above data has been obtained, you can proceed with the below formulas to calculate the limits. The below formulas are valid for all cases (Including The limitation listed above).Formulas for Limits of External Acme Thread\( \begin{array}{l} \large d_{max} = d_{nom} \\ \large d_{min} = d_{max}\,-\,T_d \\ \large d_{2\,max} = d_{2\,nom}\,-\,es \\ \large d_{2\,min} = d_{2\,max}\,-\,T_{d2} \\ \large d_{1\,max} = d_{1\,nom}\,-\,el \\ \large d_{1\,min} = d_{1\,max}\,-\,1.5 \times T_{d2} \end{array} \)Formulas for Limits of an Internal Acme Thread\( \begin{array}{l} \large D_{min} = D_{nom}\,+\,el \\ \large D_{max} = D_{min}\,+\,el \\ \large D_{2\,min} = D_{2\,nom} \\ \large D_{2\,max} = D_{2\,min}\,+\,T_{d2} \\ \large D_{1\,min} = D_{1\,nom} \\ \large D_{1\,max} = D_{1\,min}\,+\,T_{d} \end{array} \)Special ACME ThreadsBecause of the nature of its use cases and the limited list of standard configurations, special Acme threads are commonly used.What is considered a special Acme thread?A Diameter-Pitch combination that does not appear in this list.Multiple-Start threads.An engagement length that is larger than twice the major diameter.The Acme Thread Calculator  handles also Special Threads!Diameter-Pitch combinationsThe standard list of Acme threads in ASTM B1.5 has only one pitch option per diameter. However, “playing” with the pitch is an important design consideration since it allows us to increase the traverse speed by using a coarser pitch or increasing the accuracy by choosing a finer one. When opting for a special thread, ASTM B1.5 provides each pitch with the minimum and maximum allowed diameters.Premisable Diamter-Pitch CombinationsFor s thread with an intermediate pitch value, use the diameters shown for the next coarser pitch in the graph.To get the dimensions for such a thread, follow the formulas provided above or our Acme Thread Calculator, which knows how to handle any diameter-pitch combination.Multiple Start ThreadsMultiple-Start Acme threads are popular since they can bump up the traverse speed in multiples of 2, 3, 4, or more.The dimensions given in the standard are valid only for single-start threads. Use the below procedure to adjust the limits according to the number of starts.External threads (Screws) are not affected. The data for single-start threads should be used.For internal threads (Nuts), the allowance for major, minor, and pitch diameters is increased (relative to an equivalent single-start thread) by K x es. K depends on the number of starts: for 2 starts k=0.5, 3 starts k=0.75, and for 4 starts or more, k=1. Our Acme Thread Calculator also handles multiple-start threads!Length of EngagementIncreasing the length of the engagement means using a lengthier nut that can support higher forces. The data listed in ASTM B1.5 and the formulas given above are valid for engagement lengths up to twice the major diameter. The pitch diameter allowance (es) should be increased by 0.1 x es x (LE -  2 x d) when LE>2XD. Our Acme Thread Calculator also handles all engagement lengths.Related Glossary Terms:Lead (Threading)CNC MachineMajor DiameterTooth per inch (tpi)Thread Allowance (es)Minor DiameterPitch DiameterPitchThread Height (Depth)Tap Drill Size

This article aims to provide a comprehensive overview of ring main distribution system, its comparison with radial distribution system, and its relevance for various competitive exams.

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The below formulas are not valid for the following cases:Centralizes Acme series.Engagement lengths that are larger than twice the major diameter.Threads with multiple starts.TPI values that are not one of 2-6, 8, 10, 12, 14, or 16.Nominal diameters that are not one of 1/4, 5/16, 3/8, 7/16, 1/2, 3/4, 7/8, 1, 1-1/8, 1-1/4, 1-3/8, 1-1/2, 1-3/4, 2, 2-1/2, 2-3/4, 3, 3-1/2, 4, 4-1/2, or 5 Inches.For these cases, read the small print in ASTM B1.5 or use our Acme Thread Calculator  that handles all cases!Before calculating the limits, you need to obtain the following data:Allowance for major and minor diameters (el): Equals 0.002 for pitches of 10 TPI or coarser. For finer pitches, use 0.001.Allowance for pitch diameters (es): Should be obtained from ASM B1.5 (table 9). It cannot be calculated by a formula. You can either obtain it from the standard or use our below calculator.Payment options Pitch diameter tolerance (TD2): Should be obtained from ASM B1.5 (tables 5-7) or calculated with the below formula.\( TD_2 = K_P \times \sqrt{P} + K_D \times \sqrt{D} \)ClassKpKd2G / 3C0.030.0063G / 3C0.0140.00284G / 4C0.010.002Major diameter tolerance (Td): Equals to the TPI divided by 20. (But if less than 0.005, 0.005 should be used).After the above data has been obtained, you can proceed with the below formulas to calculate the limits. The below formulas are valid for all cases (Including The limitation listed above).Formulas for Limits of External Acme Thread\( \begin{array}{l} \large d_{max} = d_{nom} \\ \large d_{min} = d_{max}\,-\,T_d \\ \large d_{2\,max} = d_{2\,nom}\,-\,es \\ \large d_{2\,min} = d_{2\,max}\,-\,T_{d2} \\ \large d_{1\,max} = d_{1\,nom}\,-\,el \\ \large d_{1\,min} = d_{1\,max}\,-\,1.5 \times T_{d2} \end{array} \)Formulas for Limits of an Internal Acme Thread\( \begin{array}{l} \large D_{min} = D_{nom}\,+\,el \\ \large D_{max} = D_{min}\,+\,el \\ \large D_{2\,min} = D_{2\,nom} \\ \large D_{2\,max} = D_{2\,min}\,+\,T_{d2} \\ \large D_{1\,min} = D_{1\,nom} \\ \large D_{1\,max} = D_{1\,min}\,+\,T_{d} \end{array} \)Special ACME ThreadsBecause of the nature of its use cases and the limited list of standard configurations, special Acme threads are commonly used.What is considered a special Acme thread?A Diameter-Pitch combination that does not appear in this list.Multiple-Start threads.An engagement length that is larger than twice the major diameter.The Acme Thread Calculator  handles also Special Threads!Diameter-Pitch combinationsThe standard list of Acme threads in ASTM B1.5 has only one pitch option per diameter. However, “playing” with the pitch is an important design consideration since it allows us to increase the traverse speed by using a coarser pitch or increasing the accuracy by choosing a finer one. When opting for a special thread, ASTM B1.5 provides each pitch with the minimum and maximum allowed diameters.Premisable Diamter-Pitch CombinationsFor s thread with an intermediate pitch value, use the diameters shown for the next coarser pitch in the graph.To get the dimensions for such a thread, follow the formulas provided above or our Acme Thread Calculator, which knows how to handle any diameter-pitch combination.Multiple Start ThreadsMultiple-Start Acme threads are popular since they can bump up the traverse speed in multiples of 2, 3, 4, or more.The dimensions given in the standard are valid only for single-start threads. Use the below procedure to adjust the limits according to the number of starts.External threads (Screws) are not affected. The data for single-start threads should be used.For internal threads (Nuts), the allowance for major, minor, and pitch diameters is increased (relative to an equivalent single-start thread) by K x es. K depends on the number of starts: for 2 starts k=0.5, 3 starts k=0.75, and for 4 starts or more, k=1. Our Acme Thread Calculator also handles multiple-start threads!Length of EngagementIncreasing the length of the engagement means using a lengthier nut that can support higher forces. The data listed in ASTM B1.5 and the formulas given above are valid for engagement lengths up to twice the major diameter. The pitch diameter allowance (es) should be increased by 0.1 x es x (LE -  2 x d) when LE>2XD. Our Acme Thread Calculator also handles all engagement lengths.Related Glossary Terms:Lead (Threading)CNC MachineMajor DiameterTooth per inch (tpi)Thread Allowance (es)Minor DiameterPitch DiameterPitchThread Height (Depth)Tap Drill Size

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A ring main distribution system comprises of feeders connected in a closed loop or ring configuration, with distributors tapped from different points along the ring. The defining trait is the formation of a continuous loop network without any terminating end in the feeders.

The basic dimensions are nominal dimensions of the ACME profile without allowances and tolerances (The series and class define that – see below). They are based on standard ASTM B1.5. The basic dimensions can be used for design. However, for manufacturing and machining, you need the allowable range of each dimension. This data can be found in the ASTM standard or in the Limits and Dimensions section below. All the basic dimensions are derived from simple formulas based on the thread’s nominal diameter and pitch.SymbolsList of symbols used in charts and formulas of ACME ThreadsSymbolExplanationBasic Parameters - Diameters and PitchDMajor (Basic) diameter of internal threadD1Minor diameter of internal threadD2Pitch diameter of internal threaddExternal Major Diameterd1Minor diameter of external threadd2Pitch diameter of external threadnNumber of threds per Inch (TPI)PPitch (Distance)LLeadSNumber of StartshThread HeightFFlat WidthLELength of EngagmentαThread V half AngleAllowance, Deviation, and TolerancesTDTolerance - Minor diameter of internal thread & (Major Diameter)TD2Tolerance - Pitch diameter of internal threadTdTolerance - Minor diameter of external thread & (Major Diameter)Td2Tolerance - Minor diameter of external threadesAllowance - Pitch DiameterELAllowance - Major Diameter & (Minor Diameter)FormulasExternal Thread\( \begin{array}{l} \large d= \text{Diameter from designation} \\ \large n = \text{TPI from designation} \\ \large P = \frac{n}{TPI} \\ \large h = \frac{P}{2} \\ \large d _2= d\,-\,h \\ \large d_1 = d\,-\,P \\ \large F = 0.3707 \times P \\ \large 2\times\alpha = 29^{\circ} \\ \large \lambda = \tan^{-1} \left ( \frac{P \times S}{\pi \times d_2} \right ) \end{array} \)Internal thread\( \begin{array}{l} \large D= \text{Diameter from designation} \\ \large n = \text{TPI from designation} \\ \large P = \frac{n}{TPI} \\ \large h = \frac{P}{2} \\ \large D _2= D\,-\,h \\ \large D_1 = D\,-\,P \\ \large F = 0.3707 \times P \\ \large 2\times\alpha = 29^{\circ} \\ \large \lambda = \tan^{-1} \left ( \frac{P \times S}{\pi \times D_2} \right ) \end{array} \)Dimensions ChartClick the Thread Link to get the Full Thread Data for all classes in Inch and Metric units* Click icon to show Additional columns.(*) All dimensions are in InchesThreadMajor DiameterTPIPitchPitch DiameterMinor DiameterThread HeightFlat WidthLead AngleTap Drill Siuze1/4 - 16 ACME0.25160.06250.21880.18750.031250.02325.2°0.1875Metric Data ➢Tolerances ➢5/16 - 14 ACME0.3125140.07140.27680.24110.035710.02654.7°0.2411Metric Data ➢Tolerances ➢3/8 - 12 ACME0.375120.08330.33330.29170.041670.03094.55°0.2917Metric Data ➢Tolerances ➢7/16 - 12 ACME0.4375120.08330.39580.35420.041670.03093.83°0.3542Metric Data ➢Tolerances ➢1/2 - 10 ACME0.5100.10.450.40.050.03714.05°0.4Metric Data ➢Tolerances ➢5/8 - 8 ACME0.62580.1250.56250.50.06250.04634.05°0.5Metric Data ➢Tolerances ➢3/4 - 6 ACME0.7560.16670.66670.58330.083330.06184.55°0.5833Metric Data ➢Tolerances ➢7/8 - 6 ACME0.87560.16670.79170.70830.083330.06183.83°0.7083Metric Data ➢Tolerances ➢1 - 5 ACME150.20.90.80.10.07414.05°0.8Metric Data ➢Tolerances ➢1 1/8 - 5 ACME1.12550.21.0250.9250.10.07413.55°N/AMetric Data ➢Tolerances ➢1 1/4 - 5 ACME1.2550.21.151.050.10.07413.17°N/AMetric Data ➢Tolerances ➢1 3/8 - 4 ACME1.37540.251.251.1250.1250.09273.64°N/AMetric Data ➢Tolerances ➢1 1/2 - 4 ACME1.540.251.3751.250.1250.09273.31°N/AMetric Data ➢Tolerances ➢1 3/4 - 4 ACME1.7540.251.6251.50.1250.09272.8°N/AMetric Data ➢Tolerances ➢2 - 4 ACME240.251.8751.750.1250.09272.43°N/AMetric Data ➢Tolerances ➢2 1/4 - 3 ACME2.2530.33332.08331.91670.166670.12362.92°N/AMetric Data ➢Tolerances ➢2 1/2 - 3 ACME2.530.33332.33332.16670.166670.12362.6°N/AMetric Data ➢Tolerances ➢2 3/4 - 3 ACME2.7530.33332.58332.41670.166670.12362.35°N/AMetric Data ➢Tolerances ➢3 - 2 ACME320.52.752.50.250.18543.31°N/AMetric Data ➢Tolerances ➢3 1/2 - 2 ACME3.520.53.2530.250.18542.8°N/AMetric Data ➢Tolerances ➢4 - 2 ACME420.53.753.50.250.18542.43°N/AMetric Data ➢Tolerances ➢4 1/2 - 2 ACME4.520.54.2540.250.18542.14°N/AMetric Data ➢Tolerances ➢5 - 2 ACME520.54.754.50.250.18541.92°N/AMetric Data ➢Tolerances ➢ACME Threads – Limits of DimensionsTo manufacture or measure a thread, one has to know the maximum and minimum permissible values of the basic dimensions. These values are calculated according to the thread series and class (See below).Definition of terms:Allowance (Deviation): The minimum permissible distance between the basic and actual profile.Tolerance: The width of the tolerance field of a diameter on the actual thread profile. (Pitch, Major & Minor diameters)A small allowance means that the assembly of a male and female thread will be harder, but after assembly, there will be less freedom of movement.A large allowance means that the assembly of a male and female thread will be easier, but after assembly, there will be more freedom of movement.The allowance size does not influence a thread’s production difficulty or price.A wide tolerance is easier and cheaper to produce but yields a larger spread between threads.A narrow tolerance is challenging to produce and more expensive but yields a smaller spread between threads.Series & ClassesACME threads are divided into 3 series:G (General Purpose) – The most commonly used Acme threads. Wedging can occur under loads; therefore, it is recommended for applications where the screw and nut are supported individually.It has 3 precision classes 2G, 3G, and 4G.C (Centralized) – Tighter clearance between the internal and external threads. That prevents wedging on the flanks. More suitable for applications with higher load.It shares the exact basic dimensions of the C series. The difference is only in the tolerances.It has 3 precision classes 2C, 3C, and 4C.Stub – Compact threads with a 43% shorter stub height than standard Acme.Short and truncated thread profile, suitable for applications with limited space. Unlike G & C series, it only has a single precision class. They are defined in a separate ASTM document number B1.8.Series G & C have 3 preciosn classes:2G/2C – Least accurate and more commonly used.3G/3C – Medium accuracy.4G/4C – Highest accuracy, recommended to reduce backlash.Limits CalculationsASTM B1.5 defines how to calculate the tolerance of the following parameters:Major diameter (d / D)Minor diameter (d1 / D1)Pitch diameter (d2 / D2)Pitch & Lead (P / L)Angles between flanks (α)The below formulas are not valid for the following cases:Centralizes Acme series.Engagement lengths that are larger than twice the major diameter.Threads with multiple starts.TPI values that are not one of 2-6, 8, 10, 12, 14, or 16.Nominal diameters that are not one of 1/4, 5/16, 3/8, 7/16, 1/2, 3/4, 7/8, 1, 1-1/8, 1-1/4, 1-3/8, 1-1/2, 1-3/4, 2, 2-1/2, 2-3/4, 3, 3-1/2, 4, 4-1/2, or 5 Inches.For these cases, read the small print in ASTM B1.5 or use our Acme Thread Calculator  that handles all cases!Before calculating the limits, you need to obtain the following data:Allowance for major and minor diameters (el): Equals 0.002 for pitches of 10 TPI or coarser. For finer pitches, use 0.001.Allowance for pitch diameters (es): Should be obtained from ASM B1.5 (table 9). It cannot be calculated by a formula. You can either obtain it from the standard or use our below calculator.Payment options Pitch diameter tolerance (TD2): Should be obtained from ASM B1.5 (tables 5-7) or calculated with the below formula.\( TD_2 = K_P \times \sqrt{P} + K_D \times \sqrt{D} \)ClassKpKd2G / 3C0.030.0063G / 3C0.0140.00284G / 4C0.010.002Major diameter tolerance (Td): Equals to the TPI divided by 20. (But if less than 0.005, 0.005 should be used).After the above data has been obtained, you can proceed with the below formulas to calculate the limits. The below formulas are valid for all cases (Including The limitation listed above).Formulas for Limits of External Acme Thread\( \begin{array}{l} \large d_{max} = d_{nom} \\ \large d_{min} = d_{max}\,-\,T_d \\ \large d_{2\,max} = d_{2\,nom}\,-\,es \\ \large d_{2\,min} = d_{2\,max}\,-\,T_{d2} \\ \large d_{1\,max} = d_{1\,nom}\,-\,el \\ \large d_{1\,min} = d_{1\,max}\,-\,1.5 \times T_{d2} \end{array} \)Formulas for Limits of an Internal Acme Thread\( \begin{array}{l} \large D_{min} = D_{nom}\,+\,el \\ \large D_{max} = D_{min}\,+\,el \\ \large D_{2\,min} = D_{2\,nom} \\ \large D_{2\,max} = D_{2\,min}\,+\,T_{d2} \\ \large D_{1\,min} = D_{1\,nom} \\ \large D_{1\,max} = D_{1\,min}\,+\,T_{d} \end{array} \)Special ACME ThreadsBecause of the nature of its use cases and the limited list of standard configurations, special Acme threads are commonly used.What is considered a special Acme thread?A Diameter-Pitch combination that does not appear in this list.Multiple-Start threads.An engagement length that is larger than twice the major diameter.The Acme Thread Calculator  handles also Special Threads!Diameter-Pitch combinationsThe standard list of Acme threads in ASTM B1.5 has only one pitch option per diameter. However, “playing” with the pitch is an important design consideration since it allows us to increase the traverse speed by using a coarser pitch or increasing the accuracy by choosing a finer one. When opting for a special thread, ASTM B1.5 provides each pitch with the minimum and maximum allowed diameters.Premisable Diamter-Pitch CombinationsFor s thread with an intermediate pitch value, use the diameters shown for the next coarser pitch in the graph.To get the dimensions for such a thread, follow the formulas provided above or our Acme Thread Calculator, which knows how to handle any diameter-pitch combination.Multiple Start ThreadsMultiple-Start Acme threads are popular since they can bump up the traverse speed in multiples of 2, 3, 4, or more.The dimensions given in the standard are valid only for single-start threads. Use the below procedure to adjust the limits according to the number of starts.External threads (Screws) are not affected. The data for single-start threads should be used.For internal threads (Nuts), the allowance for major, minor, and pitch diameters is increased (relative to an equivalent single-start thread) by K x es. K depends on the number of starts: for 2 starts k=0.5, 3 starts k=0.75, and for 4 starts or more, k=1. Our Acme Thread Calculator also handles multiple-start threads!Length of EngagementIncreasing the length of the engagement means using a lengthier nut that can support higher forces. The data listed in ASTM B1.5 and the formulas given above are valid for engagement lengths up to twice the major diameter. The pitch diameter allowance (es) should be increased by 0.1 x es x (LE -  2 x d) when LE>2XD. Our Acme Thread Calculator also handles all engagement lengths.Related Glossary Terms:Lead (Threading)CNC MachineMajor DiameterTooth per inch (tpi)Thread Allowance (es)Minor DiameterPitch DiameterPitchThread Height (Depth)Tap Drill Size

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Multiple-Start Acme threads are popular since they can bump up the traverse speed in multiples of 2, 3, 4, or more.The dimensions given in the standard are valid only for single-start threads. Use the below procedure to adjust the limits according to the number of starts.External threads (Screws) are not affected. The data for single-start threads should be used.For internal threads (Nuts), the allowance for major, minor, and pitch diameters is increased (relative to an equivalent single-start thread) by K x es. K depends on the number of starts: for 2 starts k=0.5, 3 starts k=0.75, and for 4 starts or more, k=1. Our Acme Thread Calculator also handles multiple-start threads!Length of EngagementIncreasing the length of the engagement means using a lengthier nut that can support higher forces. The data listed in ASTM B1.5 and the formulas given above are valid for engagement lengths up to twice the major diameter. The pitch diameter allowance (es) should be increased by 0.1 x es x (LE -  2 x d) when LE>2XD. Our Acme Thread Calculator also handles all engagement lengths.Related Glossary Terms:Lead (Threading)CNC MachineMajor DiameterTooth per inch (tpi)Thread Allowance (es)Minor DiameterPitch DiameterPitchThread Height (Depth)Tap Drill Size