NPTF stands for “National Pipe Taper Fuel”. It is a tapered pipe thread per ASTM B 1.20.3, derived from the more common NPT standard. It is often referred to as “Dryseal thread”. The tolerances of NPTF are tighter and create a “Metal to Metal” contact between the male and female parts, thus creating a better seal without the need for sealing material. It is commonly used in hydraulic, fuel, and other applications requiring a tight, leak-proof connection.

NPTFtap

Series:NPTF, PTF, NPSF, or NPSI. Where the meaning of each letter is:N = NationalP = PipeT = TaperS = StraightF = FuelI = IntermediateAdditional Parameters:Direction: By default, the thread is right-hand. For a left-hand thread, add the suffix -LH.NPTF series – National Pipe Taper Fuel ThreadNPTF stands for National Pipe Tapered Fuel. . The basic profile is identical to the common NPT thread. The main difference is that NPTF provides a leakproof seal without using a sealant. It is obtained by tight tolerances and gauging requirements that create interference fitting in all conditions. The thread profile is tapered at an angle of 1°47′ (0.0625 Inch per inch of length) relative to the axis. Learn more about the difference between NPTF & NPT.The profile properties, such as height, pitch, and truncations, are constant. However, the pitch diameter is not a constant value. It changes depending on the distance from the beginning of the thread. Because of that, the set of parameters and measuring techniques is very different (and often confusing) compared to Unified Inch and metric threads. To make the explanations and drawings more straightforward, we split them into 3 sections:An assembly drawing of an External and Internal thread showing only the parameters that are either common to both or are relevant to the assembly.External thread drawing with all its relevant dimensions.Internal thread drawing with all its relevant dimensions.Common Dimensions (External & Internal)When assembling with “hand force”, the male and female parts of a tapered thread will turn several rotations until the clearance is closed, and a “stop” is reached. This distance is called “Hand Tight Engagement Length”, and an “L1 Gauge usually measures it”. To form the seal, the assembly continues with a wrench an additional distance called “Wrench Allowance”.NPTF Pipe & Fitting Assembly DrawingSymbolsSymbolNameExplnationPpitchGiven in TPI, and used in calculations as distanceßThread Tapper AngleEquals 1°47' (1.7833°)Defined by ASME B1.20.3 as 0.0625 +/-0.0050 inch/inchαThread V half AngleEquals 30°Tolerance is defined in the below chartHHeight of the "sharp V"The height of the theoretical profile triangle.\( H=\frac{\sqrt{3}}{2}\times{P} \)hThread HeightDistance between the truncated root and crest. It is a result of the truncation tolerances as defined in the Below Chart.L1Length of hand-tight engagementThe maximum distance that the male and female parts can be threaded by normal hand force.E1Pitch diameter at the L1 PlaneThe Pitch d diameter at the plane of hand-tight engagement length (L1) of external thread (Pipe), and at the large end of internal thread (Fitting)L1 - L2Maximum Wrenching DistanceTo create a seal, the pipe and fitting should be further tightened by a wrench beyond the L1 plane.L3Minimum Wrenching DistanceNPTF External Thread DimensionsBasic DrawingProfile DrawingSymbolsSymbolNameExplnationP, H, h, L1, E1 α, and ß are defined in the assembly section above.DPipe ODOuter diameter of the pipeE0Pitch Diameter at the Pipe's endE0=D - (O.O5*D + 1.1 ) * PL2Length of Last usefull ThreadLength of Last proper Thread. At L2, the thread profile starts to get truncated, but it is still considered "useful" until this point.E2Pitch Diameter at E2 planeE2 = E0 + 0.0625 *  L2VLength of Vanish threadsThe length of "Unuseful" threads.Basic Dimensions Chart – NPTF External ThreadsDimensions are in Inches. To view metric values, click the Thread Description link.There are a total of 20 parameters for each thread size. The below charts show only the main ones. To view all the parameters, click the thread description link.ThreadPipepipe ODTPIPitchEnd Pitch Diameter (E0)Engagement Length (L1)1/16 - 27 NPTF1/160.3125270.03700.271180.160001/8 - 27 NPTF1/80.4050270.03700.363510.161501/4 - 18 NPTF1/40.5400180.05560.477390.227803/8 - 18 NPTF3/80.6750180.05560.612010.240001/2 - 14 NPTF1/20.8400140.07140.758430.320003/4 - 14 NPTF3/41.0500140.07140.967680.339001 - 11 1/2 NPTF11.3150120.08701.213630.400001 1/4 - 11 1/2 NPTF1 1/41.6600120.08701.557130.420001 1/2 - 11 1/2 NPTF1 1/21.9000120.08701.796090.420002 - 11 1/2 NPTF22.3750120.08702.269020.436002 1/2 - 8 NPTF2 1/22.875080.12502.719530.682003 - 8 NPTF33.500080.12503.340620.76600NPTF Internal Thread DimensionsBasic DrawingProfile DrawingSymbols for NPTF Internal (Fitting Thread)SymbolNameExplnationP, H, h, L1, E1 α, and ß are defined in the assembly section above.E1Large End Pitch DiameterE1 = E0 + 0.0625 *  L1E3Small End Pitch DiameterE3 = E1 - 0.0625 *  (L1+L3)L3Length of Wrenching AllowanceTo create a seal, the pipe and fitting should be tightened by a wrench beyond the L1 plane by a minimum distance of L3.L1 + L3Thread LengthMinimum Internal Thread lengthTTap Drill SizeRecomended Drill diameter for tapping.Basic Dimensions Chart – NPTF Internal ThreadsDimensions are in Inches. To view metric values, click the Thread Description Link.There are a total of 15 parameters for each thread size. The below charts show only the main ones. To view all the parameters, click the thread description link. ThreadTPIPitchEnd Pitch Diameter (E1)Min Thread LengthTap Drill Size1/16 - 27 NPTF270.03700.281180.271100.240501/8 - 27 NPTF270.03700.373600.272600.332301/4 - 18 NPTF180.05560.491630.394500.431503/8 - 18 NPTF180.05560.627010.406700.565901/2 - 14 NPTF140.07140.778430.534300.698303/4 - 14 NPTF140.07140.988870.553300.906701 - 11 1/2 NPTF120.08701.238630.660901.139001 1/4 - 11 1/2 NPTF120.08701.583380.680901.480501 1/2 - 11 1/2 NPTF120.08701.822340.680901.717502 - 11 1/2 NPTF120.08702.296270.696902.186402 1/2 - 8 NPTF80.12502.762161.057002.605403 - 8 NPTF80.12503.388501.141003.22450Limits & Tolerances for NPTF threadsThe tolerancing system for NPTF resembles the NPT standard’s requirements but is more strict in several respects:Taper angle tolerance.Truncation tolerances.Required gauging.Taper Angle (ß) ToleranceThe taper angle (Beta) is defined in ASME B1-20.3 as 0.0625 +/-0.0050 Inch per an inch length. If we measure the pitch diameter at a particular location, move one inch along the axis and measure it again, we should measure a difference in diameter of 0.0625″.I have no idea why an angle is defined in such a peculiar way; however, you can convert it to degrees using the below formula:\( \beta = 0.5 \times \tan^{-1} \left( { 0.0625 } \right) = 1.79^{\circ}\)The linear units are measured on the diameter, and the angle is measured “per side”. Therefore the 0.5 factor is applied.The tolerance field is about 60% compared to the field in regular NPT threads.Truncation and Height TolerancesDimensions are in Inches.The ASTM standard provides only the tolerance of the truncations.We calculated the height limits based on that.The tolerances depend only on the pitch.The tolerance field is about 60% compared to the field in regular NPT threads.TPIThread HeightCrest TruncationRoot TruncationHead Anglehminhmaxfminfmaxfminfmax2α (60°)270.023380.026880.00170.00350.00350.0052+/- 2.5°180.037710.041210.00260.00430.00430.0061+/- 2°140.05140.05490.00260.00430.00430.0061+/- 2°11.50.062310.066610.00350.00520.00520.0078+/- 1.5°80.091850.096150.00520.00690.00690.0095+/- 1.5°Gauging for acceptanceThe NPT standard requires only an L1 Gage.NPTF requires, in addition to the L1 gage, also: L2, L3, and “Crest Check” gages.NPSF – Nation Pipe Straight Fuel ThreadNPSF threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered NPTF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSF threads are used with ductile materials that can adjust at assembly to the external taper during assembly.They should not be used in hard/brittle materials.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSF Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2768 - 0.28030.24820.311/8" - 27 NPSF0.3692 - 0.37270.34060.311/4" - 18 NPSF0.4852 - 0.49040.44220.473/8" - 18 NPSF0.6205 - 0.62570.57760.51/2" - 14 NPSF0.77 - 0.77670.71330.663/4" - 14 NPSF0.9805 - 0.98720.92380.661" - 11 1/2 NPSF1.2284 - 1.23651.160.78Dimensions in InchesNPSI – Nation Pipe Straight Intermediate ThreadNPSI threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered PTF-SAE short threads.They have slightly larger diameters than the NPSF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSI threads are used with hard/brittle materials that can adjust at assembly to the external taper during assembly.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSI Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2791 - 0.28260.25050.311/8" - 27 NPSF0.3715 - 0.3750.34290.311/4" - 18 NPSF0.4886 - 0.49380.44570.473/8" - 18 NPSF0.624 - 0.62920.58110.51/2" - 14 NPSF0.7745 - 0.78120.7180.663/4" - 14 NPSF0.985 - 0.99170.92830.661" - 11 1/2 NPSF1.2338 - 1.2421.16550.78Dimensions in InchesPTF-SAE Short ThreadExternalPTF-SAE Short External threads conform in all parameters with NPTF external threads, except that the thread length is shorter by one thread from the small (entering) end. They are designed for applications with limited clearance.They are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT external threads are intended for assembly with NPSI or NPTF internal threads.InternalPTF-SAE Short Internal threads conform in all parameters with NPTF internal threads, except that the thread length is shorter by one thread from the large (entering) end. They are designed for thin materials where thickness is insufficient for the full thread length of NPTFThey are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT internal threads are intended for assembly with NPTF external threads.They cannot be assembled with PTF-SAE short external threads.Related Glossary Terms:PitchL1 GagePress FitLength of EngagementDuctilityMajor DiameterTooth per inch (tpi)Pitch DiameterThread Height (Depth)Thread TruncationTap Drill SizeMinor Diameter

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NPTFthread Chart

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NPT female

To make the explanations and drawings more straightforward, we split them into 3 sections:An assembly drawing of an External and Internal thread showing only the parameters that are either common to both or are relevant to the assembly.External thread drawing with all its relevant dimensions.Internal thread drawing with all its relevant dimensions.Common Dimensions (External & Internal)When assembling with “hand force”, the male and female parts of a tapered thread will turn several rotations until the clearance is closed, and a “stop” is reached. This distance is called “Hand Tight Engagement Length”, and an “L1 Gauge usually measures it”. To form the seal, the assembly continues with a wrench an additional distance called “Wrench Allowance”.NPTF Pipe & Fitting Assembly DrawingSymbolsSymbolNameExplnationPpitchGiven in TPI, and used in calculations as distanceßThread Tapper AngleEquals 1°47' (1.7833°)Defined by ASME B1.20.3 as 0.0625 +/-0.0050 inch/inchαThread V half AngleEquals 30°Tolerance is defined in the below chartHHeight of the "sharp V"The height of the theoretical profile triangle.\( H=\frac{\sqrt{3}}{2}\times{P} \)hThread HeightDistance between the truncated root and crest. It is a result of the truncation tolerances as defined in the Below Chart.L1Length of hand-tight engagementThe maximum distance that the male and female parts can be threaded by normal hand force.E1Pitch diameter at the L1 PlaneThe Pitch d diameter at the plane of hand-tight engagement length (L1) of external thread (Pipe), and at the large end of internal thread (Fitting)L1 - L2Maximum Wrenching DistanceTo create a seal, the pipe and fitting should be further tightened by a wrench beyond the L1 plane.L3Minimum Wrenching DistanceNPTF External Thread DimensionsBasic DrawingProfile DrawingSymbolsSymbolNameExplnationP, H, h, L1, E1 α, and ß are defined in the assembly section above.DPipe ODOuter diameter of the pipeE0Pitch Diameter at the Pipe's endE0=D - (O.O5*D + 1.1 ) * PL2Length of Last usefull ThreadLength of Last proper Thread. At L2, the thread profile starts to get truncated, but it is still considered "useful" until this point.E2Pitch Diameter at E2 planeE2 = E0 + 0.0625 *  L2VLength of Vanish threadsThe length of "Unuseful" threads.Basic Dimensions Chart – NPTF External ThreadsDimensions are in Inches. To view metric values, click the Thread Description link.There are a total of 20 parameters for each thread size. The below charts show only the main ones. To view all the parameters, click the thread description link.ThreadPipepipe ODTPIPitchEnd Pitch Diameter (E0)Engagement Length (L1)1/16 - 27 NPTF1/160.3125270.03700.271180.160001/8 - 27 NPTF1/80.4050270.03700.363510.161501/4 - 18 NPTF1/40.5400180.05560.477390.227803/8 - 18 NPTF3/80.6750180.05560.612010.240001/2 - 14 NPTF1/20.8400140.07140.758430.320003/4 - 14 NPTF3/41.0500140.07140.967680.339001 - 11 1/2 NPTF11.3150120.08701.213630.400001 1/4 - 11 1/2 NPTF1 1/41.6600120.08701.557130.420001 1/2 - 11 1/2 NPTF1 1/21.9000120.08701.796090.420002 - 11 1/2 NPTF22.3750120.08702.269020.436002 1/2 - 8 NPTF2 1/22.875080.12502.719530.682003 - 8 NPTF33.500080.12503.340620.76600NPTF Internal Thread DimensionsBasic DrawingProfile DrawingSymbols for NPTF Internal (Fitting Thread)SymbolNameExplnationP, H, h, L1, E1 α, and ß are defined in the assembly section above.E1Large End Pitch DiameterE1 = E0 + 0.0625 *  L1E3Small End Pitch DiameterE3 = E1 - 0.0625 *  (L1+L3)L3Length of Wrenching AllowanceTo create a seal, the pipe and fitting should be tightened by a wrench beyond the L1 plane by a minimum distance of L3.L1 + L3Thread LengthMinimum Internal Thread lengthTTap Drill SizeRecomended Drill diameter for tapping.Basic Dimensions Chart – NPTF Internal ThreadsDimensions are in Inches. To view metric values, click the Thread Description Link.There are a total of 15 parameters for each thread size. The below charts show only the main ones. To view all the parameters, click the thread description link. ThreadTPIPitchEnd Pitch Diameter (E1)Min Thread LengthTap Drill Size1/16 - 27 NPTF270.03700.281180.271100.240501/8 - 27 NPTF270.03700.373600.272600.332301/4 - 18 NPTF180.05560.491630.394500.431503/8 - 18 NPTF180.05560.627010.406700.565901/2 - 14 NPTF140.07140.778430.534300.698303/4 - 14 NPTF140.07140.988870.553300.906701 - 11 1/2 NPTF120.08701.238630.660901.139001 1/4 - 11 1/2 NPTF120.08701.583380.680901.480501 1/2 - 11 1/2 NPTF120.08701.822340.680901.717502 - 11 1/2 NPTF120.08702.296270.696902.186402 1/2 - 8 NPTF80.12502.762161.057002.605403 - 8 NPTF80.12503.388501.141003.22450Limits & Tolerances for NPTF threadsThe tolerancing system for NPTF resembles the NPT standard’s requirements but is more strict in several respects:Taper angle tolerance.Truncation tolerances.Required gauging.Taper Angle (ß) ToleranceThe taper angle (Beta) is defined in ASME B1-20.3 as 0.0625 +/-0.0050 Inch per an inch length. If we measure the pitch diameter at a particular location, move one inch along the axis and measure it again, we should measure a difference in diameter of 0.0625″.I have no idea why an angle is defined in such a peculiar way; however, you can convert it to degrees using the below formula:\( \beta = 0.5 \times \tan^{-1} \left( { 0.0625 } \right) = 1.79^{\circ}\)The linear units are measured on the diameter, and the angle is measured “per side”. Therefore the 0.5 factor is applied.The tolerance field is about 60% compared to the field in regular NPT threads.Truncation and Height TolerancesDimensions are in Inches.The ASTM standard provides only the tolerance of the truncations.We calculated the height limits based on that.The tolerances depend only on the pitch.The tolerance field is about 60% compared to the field in regular NPT threads.TPIThread HeightCrest TruncationRoot TruncationHead Anglehminhmaxfminfmaxfminfmax2α (60°)270.023380.026880.00170.00350.00350.0052+/- 2.5°180.037710.041210.00260.00430.00430.0061+/- 2°140.05140.05490.00260.00430.00430.0061+/- 2°11.50.062310.066610.00350.00520.00520.0078+/- 1.5°80.091850.096150.00520.00690.00690.0095+/- 1.5°Gauging for acceptanceThe NPT standard requires only an L1 Gage.NPTF requires, in addition to the L1 gage, also: L2, L3, and “Crest Check” gages.NPSF – Nation Pipe Straight Fuel ThreadNPSF threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered NPTF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSF threads are used with ductile materials that can adjust at assembly to the external taper during assembly.They should not be used in hard/brittle materials.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSF Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2768 - 0.28030.24820.311/8" - 27 NPSF0.3692 - 0.37270.34060.311/4" - 18 NPSF0.4852 - 0.49040.44220.473/8" - 18 NPSF0.6205 - 0.62570.57760.51/2" - 14 NPSF0.77 - 0.77670.71330.663/4" - 14 NPSF0.9805 - 0.98720.92380.661" - 11 1/2 NPSF1.2284 - 1.23651.160.78Dimensions in InchesNPSI – Nation Pipe Straight Intermediate ThreadNPSI threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered PTF-SAE short threads.They have slightly larger diameters than the NPSF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSI threads are used with hard/brittle materials that can adjust at assembly to the external taper during assembly.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSI Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2791 - 0.28260.25050.311/8" - 27 NPSF0.3715 - 0.3750.34290.311/4" - 18 NPSF0.4886 - 0.49380.44570.473/8" - 18 NPSF0.624 - 0.62920.58110.51/2" - 14 NPSF0.7745 - 0.78120.7180.663/4" - 14 NPSF0.985 - 0.99170.92830.661" - 11 1/2 NPSF1.2338 - 1.2421.16550.78Dimensions in InchesPTF-SAE Short ThreadExternalPTF-SAE Short External threads conform in all parameters with NPTF external threads, except that the thread length is shorter by one thread from the small (entering) end. They are designed for applications with limited clearance.They are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT external threads are intended for assembly with NPSI or NPTF internal threads.InternalPTF-SAE Short Internal threads conform in all parameters with NPTF internal threads, except that the thread length is shorter by one thread from the large (entering) end. They are designed for thin materials where thickness is insufficient for the full thread length of NPTFThey are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT internal threads are intended for assembly with NPTF external threads.They cannot be assembled with PTF-SAE short external threads.Related Glossary Terms:PitchL1 GagePress FitLength of EngagementDuctilityMajor DiameterTooth per inch (tpi)Pitch DiameterThread Height (Depth)Thread TruncationTap Drill SizeMinor Diameter

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Are NPT andNPTFcompatible

ExternalPTF-SAE Short External threads conform in all parameters with NPTF external threads, except that the thread length is shorter by one thread from the small (entering) end. They are designed for applications with limited clearance.They are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT external threads are intended for assembly with NPSI or NPTF internal threads.InternalPTF-SAE Short Internal threads conform in all parameters with NPTF internal threads, except that the thread length is shorter by one thread from the large (entering) end. They are designed for thin materials where thickness is insufficient for the full thread length of NPTFThey are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT internal threads are intended for assembly with NPTF external threads.They cannot be assembled with PTF-SAE short external threads.Related Glossary Terms:PitchL1 GagePress FitLength of EngagementDuctilityMajor DiameterTooth per inch (tpi)Pitch DiameterThread Height (Depth)Thread TruncationTap Drill SizeMinor Diameter

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Diameter:The diameters are given in inch fractions. For example, 1/4″, 3/4″, and 1 1/4″.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″).It is also allowed to denote the pitch by distance. For example, 1/4-0.05P means a thread with a pitch of 0.05″ (same as 20 TPI).Series:NPTF, PTF, NPSF, or NPSI. Where the meaning of each letter is:N = NationalP = PipeT = TaperS = StraightF = FuelI = IntermediateAdditional Parameters:Direction: By default, the thread is right-hand. For a left-hand thread, add the suffix -LH.NPTF series – National Pipe Taper Fuel ThreadNPTF stands for National Pipe Tapered Fuel. . The basic profile is identical to the common NPT thread. The main difference is that NPTF provides a leakproof seal without using a sealant. It is obtained by tight tolerances and gauging requirements that create interference fitting in all conditions. The thread profile is tapered at an angle of 1°47′ (0.0625 Inch per inch of length) relative to the axis. Learn more about the difference between NPTF & NPT.The profile properties, such as height, pitch, and truncations, are constant. However, the pitch diameter is not a constant value. It changes depending on the distance from the beginning of the thread. Because of that, the set of parameters and measuring techniques is very different (and often confusing) compared to Unified Inch and metric threads. To make the explanations and drawings more straightforward, we split them into 3 sections:An assembly drawing of an External and Internal thread showing only the parameters that are either common to both or are relevant to the assembly.External thread drawing with all its relevant dimensions.Internal thread drawing with all its relevant dimensions.Common Dimensions (External & Internal)When assembling with “hand force”, the male and female parts of a tapered thread will turn several rotations until the clearance is closed, and a “stop” is reached. This distance is called “Hand Tight Engagement Length”, and an “L1 Gauge usually measures it”. To form the seal, the assembly continues with a wrench an additional distance called “Wrench Allowance”.NPTF Pipe & Fitting Assembly DrawingSymbolsSymbolNameExplnationPpitchGiven in TPI, and used in calculations as distanceßThread Tapper AngleEquals 1°47' (1.7833°)Defined by ASME B1.20.3 as 0.0625 +/-0.0050 inch/inchαThread V half AngleEquals 30°Tolerance is defined in the below chartHHeight of the "sharp V"The height of the theoretical profile triangle.\( H=\frac{\sqrt{3}}{2}\times{P} \)hThread HeightDistance between the truncated root and crest. It is a result of the truncation tolerances as defined in the Below Chart.L1Length of hand-tight engagementThe maximum distance that the male and female parts can be threaded by normal hand force.E1Pitch diameter at the L1 PlaneThe Pitch d diameter at the plane of hand-tight engagement length (L1) of external thread (Pipe), and at the large end of internal thread (Fitting)L1 - L2Maximum Wrenching DistanceTo create a seal, the pipe and fitting should be further tightened by a wrench beyond the L1 plane.L3Minimum Wrenching DistanceNPTF External Thread DimensionsBasic DrawingProfile DrawingSymbolsSymbolNameExplnationP, H, h, L1, E1 α, and ß are defined in the assembly section above.DPipe ODOuter diameter of the pipeE0Pitch Diameter at the Pipe's endE0=D - (O.O5*D + 1.1 ) * PL2Length of Last usefull ThreadLength of Last proper Thread. At L2, the thread profile starts to get truncated, but it is still considered "useful" until this point.E2Pitch Diameter at E2 planeE2 = E0 + 0.0625 *  L2VLength of Vanish threadsThe length of "Unuseful" threads.Basic Dimensions Chart – NPTF External ThreadsDimensions are in Inches. To view metric values, click the Thread Description link.There are a total of 20 parameters for each thread size. The below charts show only the main ones. To view all the parameters, click the thread description link.ThreadPipepipe ODTPIPitchEnd Pitch Diameter (E0)Engagement Length (L1)1/16 - 27 NPTF1/160.3125270.03700.271180.160001/8 - 27 NPTF1/80.4050270.03700.363510.161501/4 - 18 NPTF1/40.5400180.05560.477390.227803/8 - 18 NPTF3/80.6750180.05560.612010.240001/2 - 14 NPTF1/20.8400140.07140.758430.320003/4 - 14 NPTF3/41.0500140.07140.967680.339001 - 11 1/2 NPTF11.3150120.08701.213630.400001 1/4 - 11 1/2 NPTF1 1/41.6600120.08701.557130.420001 1/2 - 11 1/2 NPTF1 1/21.9000120.08701.796090.420002 - 11 1/2 NPTF22.3750120.08702.269020.436002 1/2 - 8 NPTF2 1/22.875080.12502.719530.682003 - 8 NPTF33.500080.12503.340620.76600NPTF Internal Thread DimensionsBasic DrawingProfile DrawingSymbols for NPTF Internal (Fitting Thread)SymbolNameExplnationP, H, h, L1, E1 α, and ß are defined in the assembly section above.E1Large End Pitch DiameterE1 = E0 + 0.0625 *  L1E3Small End Pitch DiameterE3 = E1 - 0.0625 *  (L1+L3)L3Length of Wrenching AllowanceTo create a seal, the pipe and fitting should be tightened by a wrench beyond the L1 plane by a minimum distance of L3.L1 + L3Thread LengthMinimum Internal Thread lengthTTap Drill SizeRecomended Drill diameter for tapping.Basic Dimensions Chart – NPTF Internal ThreadsDimensions are in Inches. To view metric values, click the Thread Description Link.There are a total of 15 parameters for each thread size. The below charts show only the main ones. To view all the parameters, click the thread description link. ThreadTPIPitchEnd Pitch Diameter (E1)Min Thread LengthTap Drill Size1/16 - 27 NPTF270.03700.281180.271100.240501/8 - 27 NPTF270.03700.373600.272600.332301/4 - 18 NPTF180.05560.491630.394500.431503/8 - 18 NPTF180.05560.627010.406700.565901/2 - 14 NPTF140.07140.778430.534300.698303/4 - 14 NPTF140.07140.988870.553300.906701 - 11 1/2 NPTF120.08701.238630.660901.139001 1/4 - 11 1/2 NPTF120.08701.583380.680901.480501 1/2 - 11 1/2 NPTF120.08701.822340.680901.717502 - 11 1/2 NPTF120.08702.296270.696902.186402 1/2 - 8 NPTF80.12502.762161.057002.605403 - 8 NPTF80.12503.388501.141003.22450Limits & Tolerances for NPTF threadsThe tolerancing system for NPTF resembles the NPT standard’s requirements but is more strict in several respects:Taper angle tolerance.Truncation tolerances.Required gauging.Taper Angle (ß) ToleranceThe taper angle (Beta) is defined in ASME B1-20.3 as 0.0625 +/-0.0050 Inch per an inch length. If we measure the pitch diameter at a particular location, move one inch along the axis and measure it again, we should measure a difference in diameter of 0.0625″.I have no idea why an angle is defined in such a peculiar way; however, you can convert it to degrees using the below formula:\( \beta = 0.5 \times \tan^{-1} \left( { 0.0625 } \right) = 1.79^{\circ}\)The linear units are measured on the diameter, and the angle is measured “per side”. Therefore the 0.5 factor is applied.The tolerance field is about 60% compared to the field in regular NPT threads.Truncation and Height TolerancesDimensions are in Inches.The ASTM standard provides only the tolerance of the truncations.We calculated the height limits based on that.The tolerances depend only on the pitch.The tolerance field is about 60% compared to the field in regular NPT threads.TPIThread HeightCrest TruncationRoot TruncationHead Anglehminhmaxfminfmaxfminfmax2α (60°)270.023380.026880.00170.00350.00350.0052+/- 2.5°180.037710.041210.00260.00430.00430.0061+/- 2°140.05140.05490.00260.00430.00430.0061+/- 2°11.50.062310.066610.00350.00520.00520.0078+/- 1.5°80.091850.096150.00520.00690.00690.0095+/- 1.5°Gauging for acceptanceThe NPT standard requires only an L1 Gage.NPTF requires, in addition to the L1 gage, also: L2, L3, and “Crest Check” gages.NPSF – Nation Pipe Straight Fuel ThreadNPSF threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered NPTF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSF threads are used with ductile materials that can adjust at assembly to the external taper during assembly.They should not be used in hard/brittle materials.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSF Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2768 - 0.28030.24820.311/8" - 27 NPSF0.3692 - 0.37270.34060.311/4" - 18 NPSF0.4852 - 0.49040.44220.473/8" - 18 NPSF0.6205 - 0.62570.57760.51/2" - 14 NPSF0.77 - 0.77670.71330.663/4" - 14 NPSF0.9805 - 0.98720.92380.661" - 11 1/2 NPSF1.2284 - 1.23651.160.78Dimensions in InchesNPSI – Nation Pipe Straight Intermediate ThreadNPSI threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered PTF-SAE short threads.They have slightly larger diameters than the NPSF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSI threads are used with hard/brittle materials that can adjust at assembly to the external taper during assembly.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSI Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2791 - 0.28260.25050.311/8" - 27 NPSF0.3715 - 0.3750.34290.311/4" - 18 NPSF0.4886 - 0.49380.44570.473/8" - 18 NPSF0.624 - 0.62920.58110.51/2" - 14 NPSF0.7745 - 0.78120.7180.663/4" - 14 NPSF0.985 - 0.99170.92830.661" - 11 1/2 NPSF1.2338 - 1.2421.16550.78Dimensions in InchesPTF-SAE Short ThreadExternalPTF-SAE Short External threads conform in all parameters with NPTF external threads, except that the thread length is shorter by one thread from the small (entering) end. They are designed for applications with limited clearance.They are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT external threads are intended for assembly with NPSI or NPTF internal threads.InternalPTF-SAE Short Internal threads conform in all parameters with NPTF internal threads, except that the thread length is shorter by one thread from the large (entering) end. They are designed for thin materials where thickness is insufficient for the full thread length of NPTFThey are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT internal threads are intended for assembly with NPTF external threads.They cannot be assembled with PTF-SAE short external threads.Related Glossary Terms:PitchL1 GagePress FitLength of EngagementDuctilityMajor DiameterTooth per inch (tpi)Pitch DiameterThread Height (Depth)Thread TruncationTap Drill SizeMinor Diameter

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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″).It is also allowed to denote the pitch by distance. For example, 1/4-0.05P means a thread with a pitch of 0.05″ (same as 20 TPI).Series:NPTF, PTF, NPSF, or NPSI. Where the meaning of each letter is:N = NationalP = PipeT = TaperS = StraightF = FuelI = IntermediateAdditional Parameters:Direction: By default, the thread is right-hand. For a left-hand thread, add the suffix -LH.NPTF series – National Pipe Taper Fuel ThreadNPTF stands for National Pipe Tapered Fuel. . The basic profile is identical to the common NPT thread. The main difference is that NPTF provides a leakproof seal without using a sealant. It is obtained by tight tolerances and gauging requirements that create interference fitting in all conditions. The thread profile is tapered at an angle of 1°47′ (0.0625 Inch per inch of length) relative to the axis. Learn more about the difference between NPTF & NPT.The profile properties, such as height, pitch, and truncations, are constant. However, the pitch diameter is not a constant value. It changes depending on the distance from the beginning of the thread. Because of that, the set of parameters and measuring techniques is very different (and often confusing) compared to Unified Inch and metric threads. To make the explanations and drawings more straightforward, we split them into 3 sections:An assembly drawing of an External and Internal thread showing only the parameters that are either common to both or are relevant to the assembly.External thread drawing with all its relevant dimensions.Internal thread drawing with all its relevant dimensions.Common Dimensions (External & Internal)When assembling with “hand force”, the male and female parts of a tapered thread will turn several rotations until the clearance is closed, and a “stop” is reached. This distance is called “Hand Tight Engagement Length”, and an “L1 Gauge usually measures it”. To form the seal, the assembly continues with a wrench an additional distance called “Wrench Allowance”.NPTF Pipe & Fitting Assembly DrawingSymbolsSymbolNameExplnationPpitchGiven in TPI, and used in calculations as distanceßThread Tapper AngleEquals 1°47' (1.7833°)Defined by ASME B1.20.3 as 0.0625 +/-0.0050 inch/inchαThread V half AngleEquals 30°Tolerance is defined in the below chartHHeight of the "sharp V"The height of the theoretical profile triangle.\( H=\frac{\sqrt{3}}{2}\times{P} \)hThread HeightDistance between the truncated root and crest. It is a result of the truncation tolerances as defined in the Below Chart.L1Length of hand-tight engagementThe maximum distance that the male and female parts can be threaded by normal hand force.E1Pitch diameter at the L1 PlaneThe Pitch d diameter at the plane of hand-tight engagement length (L1) of external thread (Pipe), and at the large end of internal thread (Fitting)L1 - L2Maximum Wrenching DistanceTo create a seal, the pipe and fitting should be further tightened by a wrench beyond the L1 plane.L3Minimum Wrenching DistanceNPTF External Thread DimensionsBasic DrawingProfile DrawingSymbolsSymbolNameExplnationP, H, h, L1, E1 α, and ß are defined in the assembly section above.DPipe ODOuter diameter of the pipeE0Pitch Diameter at the Pipe's endE0=D - (O.O5*D + 1.1 ) * PL2Length of Last usefull ThreadLength of Last proper Thread. At L2, the thread profile starts to get truncated, but it is still considered "useful" until this point.E2Pitch Diameter at E2 planeE2 = E0 + 0.0625 *  L2VLength of Vanish threadsThe length of "Unuseful" threads.Basic Dimensions Chart – NPTF External ThreadsDimensions are in Inches. To view metric values, click the Thread Description link.There are a total of 20 parameters for each thread size. The below charts show only the main ones. To view all the parameters, click the thread description link.ThreadPipepipe ODTPIPitchEnd Pitch Diameter (E0)Engagement Length (L1)1/16 - 27 NPTF1/160.3125270.03700.271180.160001/8 - 27 NPTF1/80.4050270.03700.363510.161501/4 - 18 NPTF1/40.5400180.05560.477390.227803/8 - 18 NPTF3/80.6750180.05560.612010.240001/2 - 14 NPTF1/20.8400140.07140.758430.320003/4 - 14 NPTF3/41.0500140.07140.967680.339001 - 11 1/2 NPTF11.3150120.08701.213630.400001 1/4 - 11 1/2 NPTF1 1/41.6600120.08701.557130.420001 1/2 - 11 1/2 NPTF1 1/21.9000120.08701.796090.420002 - 11 1/2 NPTF22.3750120.08702.269020.436002 1/2 - 8 NPTF2 1/22.875080.12502.719530.682003 - 8 NPTF33.500080.12503.340620.76600NPTF Internal Thread DimensionsBasic DrawingProfile DrawingSymbols for NPTF Internal (Fitting Thread)SymbolNameExplnationP, H, h, L1, E1 α, and ß are defined in the assembly section above.E1Large End Pitch DiameterE1 = E0 + 0.0625 *  L1E3Small End Pitch DiameterE3 = E1 - 0.0625 *  (L1+L3)L3Length of Wrenching AllowanceTo create a seal, the pipe and fitting should be tightened by a wrench beyond the L1 plane by a minimum distance of L3.L1 + L3Thread LengthMinimum Internal Thread lengthTTap Drill SizeRecomended Drill diameter for tapping.Basic Dimensions Chart – NPTF Internal ThreadsDimensions are in Inches. To view metric values, click the Thread Description Link.There are a total of 15 parameters for each thread size. The below charts show only the main ones. To view all the parameters, click the thread description link. ThreadTPIPitchEnd Pitch Diameter (E1)Min Thread LengthTap Drill Size1/16 - 27 NPTF270.03700.281180.271100.240501/8 - 27 NPTF270.03700.373600.272600.332301/4 - 18 NPTF180.05560.491630.394500.431503/8 - 18 NPTF180.05560.627010.406700.565901/2 - 14 NPTF140.07140.778430.534300.698303/4 - 14 NPTF140.07140.988870.553300.906701 - 11 1/2 NPTF120.08701.238630.660901.139001 1/4 - 11 1/2 NPTF120.08701.583380.680901.480501 1/2 - 11 1/2 NPTF120.08701.822340.680901.717502 - 11 1/2 NPTF120.08702.296270.696902.186402 1/2 - 8 NPTF80.12502.762161.057002.605403 - 8 NPTF80.12503.388501.141003.22450Limits & Tolerances for NPTF threadsThe tolerancing system for NPTF resembles the NPT standard’s requirements but is more strict in several respects:Taper angle tolerance.Truncation tolerances.Required gauging.Taper Angle (ß) ToleranceThe taper angle (Beta) is defined in ASME B1-20.3 as 0.0625 +/-0.0050 Inch per an inch length. If we measure the pitch diameter at a particular location, move one inch along the axis and measure it again, we should measure a difference in diameter of 0.0625″.I have no idea why an angle is defined in such a peculiar way; however, you can convert it to degrees using the below formula:\( \beta = 0.5 \times \tan^{-1} \left( { 0.0625 } \right) = 1.79^{\circ}\)The linear units are measured on the diameter, and the angle is measured “per side”. Therefore the 0.5 factor is applied.The tolerance field is about 60% compared to the field in regular NPT threads.Truncation and Height TolerancesDimensions are in Inches.The ASTM standard provides only the tolerance of the truncations.We calculated the height limits based on that.The tolerances depend only on the pitch.The tolerance field is about 60% compared to the field in regular NPT threads.TPIThread HeightCrest TruncationRoot TruncationHead Anglehminhmaxfminfmaxfminfmax2α (60°)270.023380.026880.00170.00350.00350.0052+/- 2.5°180.037710.041210.00260.00430.00430.0061+/- 2°140.05140.05490.00260.00430.00430.0061+/- 2°11.50.062310.066610.00350.00520.00520.0078+/- 1.5°80.091850.096150.00520.00690.00690.0095+/- 1.5°Gauging for acceptanceThe NPT standard requires only an L1 Gage.NPTF requires, in addition to the L1 gage, also: L2, L3, and “Crest Check” gages.NPSF – Nation Pipe Straight Fuel ThreadNPSF threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered NPTF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSF threads are used with ductile materials that can adjust at assembly to the external taper during assembly.They should not be used in hard/brittle materials.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSF Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2768 - 0.28030.24820.311/8" - 27 NPSF0.3692 - 0.37270.34060.311/4" - 18 NPSF0.4852 - 0.49040.44220.473/8" - 18 NPSF0.6205 - 0.62570.57760.51/2" - 14 NPSF0.77 - 0.77670.71330.663/4" - 14 NPSF0.9805 - 0.98720.92380.661" - 11 1/2 NPSF1.2284 - 1.23651.160.78Dimensions in InchesNPSI – Nation Pipe Straight Intermediate ThreadNPSI threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered PTF-SAE short threads.They have slightly larger diameters than the NPSF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSI threads are used with hard/brittle materials that can adjust at assembly to the external taper during assembly.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSI Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2791 - 0.28260.25050.311/8" - 27 NPSF0.3715 - 0.3750.34290.311/4" - 18 NPSF0.4886 - 0.49380.44570.473/8" - 18 NPSF0.624 - 0.62920.58110.51/2" - 14 NPSF0.7745 - 0.78120.7180.663/4" - 14 NPSF0.985 - 0.99170.92830.661" - 11 1/2 NPSF1.2338 - 1.2421.16550.78Dimensions in InchesPTF-SAE Short ThreadExternalPTF-SAE Short External threads conform in all parameters with NPTF external threads, except that the thread length is shorter by one thread from the small (entering) end. They are designed for applications with limited clearance.They are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT external threads are intended for assembly with NPSI or NPTF internal threads.InternalPTF-SAE Short Internal threads conform in all parameters with NPTF internal threads, except that the thread length is shorter by one thread from the large (entering) end. They are designed for thin materials where thickness is insufficient for the full thread length of NPTFThey are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT internal threads are intended for assembly with NPTF external threads.They cannot be assembled with PTF-SAE short external threads.Related Glossary Terms:PitchL1 GagePress FitLength of EngagementDuctilityMajor DiameterTooth per inch (tpi)Pitch DiameterThread Height (Depth)Thread TruncationTap Drill SizeMinor Diameter

InternalPTF-SAE Short Internal threads conform in all parameters with NPTF internal threads, except that the thread length is shorter by one thread from the large (entering) end. They are designed for thin materials where thickness is insufficient for the full thread length of NPTFThey are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT internal threads are intended for assembly with NPTF external threads.They cannot be assembled with PTF-SAE short external threads.Related Glossary Terms:PitchL1 GagePress FitLength of EngagementDuctilityMajor DiameterTooth per inch (tpi)Pitch DiameterThread Height (Depth)Thread TruncationTap Drill SizeMinor Diameter

NPTF stands for National Pipe Tapered Fuel. . The basic profile is identical to the common NPT thread. The main difference is that NPTF provides a leakproof seal without using a sealant. It is obtained by tight tolerances and gauging requirements that create interference fitting in all conditions. The thread profile is tapered at an angle of 1°47′ (0.0625 Inch per inch of length) relative to the axis. Learn more about the difference between NPTF & NPT.The profile properties, such as height, pitch, and truncations, are constant. However, the pitch diameter is not a constant value. It changes depending on the distance from the beginning of the thread. Because of that, the set of parameters and measuring techniques is very different (and often confusing) compared to Unified Inch and metric threads. To make the explanations and drawings more straightforward, we split them into 3 sections:An assembly drawing of an External and Internal thread showing only the parameters that are either common to both or are relevant to the assembly.External thread drawing with all its relevant dimensions.Internal thread drawing with all its relevant dimensions.Common Dimensions (External & Internal)When assembling with “hand force”, the male and female parts of a tapered thread will turn several rotations until the clearance is closed, and a “stop” is reached. This distance is called “Hand Tight Engagement Length”, and an “L1 Gauge usually measures it”. To form the seal, the assembly continues with a wrench an additional distance called “Wrench Allowance”.NPTF Pipe & Fitting Assembly DrawingSymbolsSymbolNameExplnationPpitchGiven in TPI, and used in calculations as distanceßThread Tapper AngleEquals 1°47' (1.7833°)Defined by ASME B1.20.3 as 0.0625 +/-0.0050 inch/inchαThread V half AngleEquals 30°Tolerance is defined in the below chartHHeight of the "sharp V"The height of the theoretical profile triangle.\( H=\frac{\sqrt{3}}{2}\times{P} \)hThread HeightDistance between the truncated root and crest. It is a result of the truncation tolerances as defined in the Below Chart.L1Length of hand-tight engagementThe maximum distance that the male and female parts can be threaded by normal hand force.E1Pitch diameter at the L1 PlaneThe Pitch d diameter at the plane of hand-tight engagement length (L1) of external thread (Pipe), and at the large end of internal thread (Fitting)L1 - L2Maximum Wrenching DistanceTo create a seal, the pipe and fitting should be further tightened by a wrench beyond the L1 plane.L3Minimum Wrenching DistanceNPTF External Thread DimensionsBasic DrawingProfile DrawingSymbolsSymbolNameExplnationP, H, h, L1, E1 α, and ß are defined in the assembly section above.DPipe ODOuter diameter of the pipeE0Pitch Diameter at the Pipe's endE0=D - (O.O5*D + 1.1 ) * PL2Length of Last usefull ThreadLength of Last proper Thread. At L2, the thread profile starts to get truncated, but it is still considered "useful" until this point.E2Pitch Diameter at E2 planeE2 = E0 + 0.0625 *  L2VLength of Vanish threadsThe length of "Unuseful" threads.Basic Dimensions Chart – NPTF External ThreadsDimensions are in Inches. To view metric values, click the Thread Description link.There are a total of 20 parameters for each thread size. The below charts show only the main ones. To view all the parameters, click the thread description link.ThreadPipepipe ODTPIPitchEnd Pitch Diameter (E0)Engagement Length (L1)1/16 - 27 NPTF1/160.3125270.03700.271180.160001/8 - 27 NPTF1/80.4050270.03700.363510.161501/4 - 18 NPTF1/40.5400180.05560.477390.227803/8 - 18 NPTF3/80.6750180.05560.612010.240001/2 - 14 NPTF1/20.8400140.07140.758430.320003/4 - 14 NPTF3/41.0500140.07140.967680.339001 - 11 1/2 NPTF11.3150120.08701.213630.400001 1/4 - 11 1/2 NPTF1 1/41.6600120.08701.557130.420001 1/2 - 11 1/2 NPTF1 1/21.9000120.08701.796090.420002 - 11 1/2 NPTF22.3750120.08702.269020.436002 1/2 - 8 NPTF2 1/22.875080.12502.719530.682003 - 8 NPTF33.500080.12503.340620.76600NPTF Internal Thread DimensionsBasic DrawingProfile DrawingSymbols for NPTF Internal (Fitting Thread)SymbolNameExplnationP, H, h, L1, E1 α, and ß are defined in the assembly section above.E1Large End Pitch DiameterE1 = E0 + 0.0625 *  L1E3Small End Pitch DiameterE3 = E1 - 0.0625 *  (L1+L3)L3Length of Wrenching AllowanceTo create a seal, the pipe and fitting should be tightened by a wrench beyond the L1 plane by a minimum distance of L3.L1 + L3Thread LengthMinimum Internal Thread lengthTTap Drill SizeRecomended Drill diameter for tapping.Basic Dimensions Chart – NPTF Internal ThreadsDimensions are in Inches. To view metric values, click the Thread Description Link.There are a total of 15 parameters for each thread size. The below charts show only the main ones. To view all the parameters, click the thread description link. ThreadTPIPitchEnd Pitch Diameter (E1)Min Thread LengthTap Drill Size1/16 - 27 NPTF270.03700.281180.271100.240501/8 - 27 NPTF270.03700.373600.272600.332301/4 - 18 NPTF180.05560.491630.394500.431503/8 - 18 NPTF180.05560.627010.406700.565901/2 - 14 NPTF140.07140.778430.534300.698303/4 - 14 NPTF140.07140.988870.553300.906701 - 11 1/2 NPTF120.08701.238630.660901.139001 1/4 - 11 1/2 NPTF120.08701.583380.680901.480501 1/2 - 11 1/2 NPTF120.08701.822340.680901.717502 - 11 1/2 NPTF120.08702.296270.696902.186402 1/2 - 8 NPTF80.12502.762161.057002.605403 - 8 NPTF80.12503.388501.141003.22450Limits & Tolerances for NPTF threadsThe tolerancing system for NPTF resembles the NPT standard’s requirements but is more strict in several respects:Taper angle tolerance.Truncation tolerances.Required gauging.Taper Angle (ß) ToleranceThe taper angle (Beta) is defined in ASME B1-20.3 as 0.0625 +/-0.0050 Inch per an inch length. If we measure the pitch diameter at a particular location, move one inch along the axis and measure it again, we should measure a difference in diameter of 0.0625″.I have no idea why an angle is defined in such a peculiar way; however, you can convert it to degrees using the below formula:\( \beta = 0.5 \times \tan^{-1} \left( { 0.0625 } \right) = 1.79^{\circ}\)The linear units are measured on the diameter, and the angle is measured “per side”. Therefore the 0.5 factor is applied.The tolerance field is about 60% compared to the field in regular NPT threads.Truncation and Height TolerancesDimensions are in Inches.The ASTM standard provides only the tolerance of the truncations.We calculated the height limits based on that.The tolerances depend only on the pitch.The tolerance field is about 60% compared to the field in regular NPT threads.TPIThread HeightCrest TruncationRoot TruncationHead Anglehminhmaxfminfmaxfminfmax2α (60°)270.023380.026880.00170.00350.00350.0052+/- 2.5°180.037710.041210.00260.00430.00430.0061+/- 2°140.05140.05490.00260.00430.00430.0061+/- 2°11.50.062310.066610.00350.00520.00520.0078+/- 1.5°80.091850.096150.00520.00690.00690.0095+/- 1.5°Gauging for acceptanceThe NPT standard requires only an L1 Gage.NPTF requires, in addition to the L1 gage, also: L2, L3, and “Crest Check” gages.NPSF – Nation Pipe Straight Fuel ThreadNPSF threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered NPTF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSF threads are used with ductile materials that can adjust at assembly to the external taper during assembly.They should not be used in hard/brittle materials.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSF Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2768 - 0.28030.24820.311/8" - 27 NPSF0.3692 - 0.37270.34060.311/4" - 18 NPSF0.4852 - 0.49040.44220.473/8" - 18 NPSF0.6205 - 0.62570.57760.51/2" - 14 NPSF0.77 - 0.77670.71330.663/4" - 14 NPSF0.9805 - 0.98720.92380.661" - 11 1/2 NPSF1.2284 - 1.23651.160.78Dimensions in InchesNPSI – Nation Pipe Straight Intermediate ThreadNPSI threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered PTF-SAE short threads.They have slightly larger diameters than the NPSF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSI threads are used with hard/brittle materials that can adjust at assembly to the external taper during assembly.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSI Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2791 - 0.28260.25050.311/8" - 27 NPSF0.3715 - 0.3750.34290.311/4" - 18 NPSF0.4886 - 0.49380.44570.473/8" - 18 NPSF0.624 - 0.62920.58110.51/2" - 14 NPSF0.7745 - 0.78120.7180.663/4" - 14 NPSF0.985 - 0.99170.92830.661" - 11 1/2 NPSF1.2338 - 1.2421.16550.78Dimensions in InchesPTF-SAE Short ThreadExternalPTF-SAE Short External threads conform in all parameters with NPTF external threads, except that the thread length is shorter by one thread from the small (entering) end. They are designed for applications with limited clearance.They are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT external threads are intended for assembly with NPSI or NPTF internal threads.InternalPTF-SAE Short Internal threads conform in all parameters with NPTF internal threads, except that the thread length is shorter by one thread from the large (entering) end. They are designed for thin materials where thickness is insufficient for the full thread length of NPTFThey are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT internal threads are intended for assembly with NPTF external threads.They cannot be assembled with PTF-SAE short external threads.Related Glossary Terms:PitchL1 GagePress FitLength of EngagementDuctilityMajor DiameterTooth per inch (tpi)Pitch DiameterThread Height (Depth)Thread TruncationTap Drill SizeMinor Diameter

The nominal taper angle is 1.709° for both standards. However, the tolerance field in NPTF is 0.3°, and NPT 0.5°. The outcome of both the taper and the truncation having tighter control leads to higher repeatability of sealing performance when using NPTF threads.Gauging for acceptanceThe NPT standard requires only an L1 Gage.NPTF requires, in addition to the L1 gage, also: L2, L3, and “Crest Check” gages.Production CostMachining: The production process for NTF and NPT is the same. Therefore the machining cost is identical.Inspection: The NPTF standard requires 3 gaging tests for acceptance (Only one in NPT). Therefore the inspection cost of NPTF is higher.Quality: The scrap rate in the production of NPTF threads is higher. An unattentive worker can easily produce nonconforming parts. This is the most significant factor that increases the cost of NPTF threads.Sealing PerformanceNPTF root and crest truncation tolerances are adjusted for an interference fit which creates a mechanical seal through thread form deformation at assembly. There is no need for PTFE, Teflon tapes, or any other sealant.NPT needs a sealant to be leak-free. A sealing material such as PTFE or Teflon must be used to prevent leaks.When is it necessary to use a mechanical seal?Using sealants could contaminate the fluids or gasses flowing through the system.A sealant might fail because of high heat or high pressure.List of Series defined in ASME B1-20.3NameDescriptionNPTFNational Pipe Taper FuelThe primary series for all service conditions.PTF-SAE ShortShort Pipe Tapar FuelSaves raw material where a full thread engagement length is not criticalNPSFNational Pipe Straight FuelInternal only straight thread for ductile materialsNPSINational Pipe Straight IntermediateInternal only straight thread for hard materialsDesignations of Dryseal Pipe ThreadsBasic designation syntax:Nominal Diameter in Inch FractionPitch in TPISeries: NPTF / PTF-SAE / NPSF / NPSI.DirectionDiameter:The diameters are given in inch fractions. For example, 1/4″, 3/4″, and 1 1/4″.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″).It is also allowed to denote the pitch by distance. For example, 1/4-0.05P means a thread with a pitch of 0.05″ (same as 20 TPI).Series:NPTF, PTF, NPSF, or NPSI. Where the meaning of each letter is:N = NationalP = PipeT = TaperS = StraightF = FuelI = IntermediateAdditional Parameters:Direction: By default, the thread is right-hand. For a left-hand thread, add the suffix -LH.NPTF series – National Pipe Taper Fuel ThreadNPTF stands for National Pipe Tapered Fuel. . The basic profile is identical to the common NPT thread. The main difference is that NPTF provides a leakproof seal without using a sealant. It is obtained by tight tolerances and gauging requirements that create interference fitting in all conditions. The thread profile is tapered at an angle of 1°47′ (0.0625 Inch per inch of length) relative to the axis. Learn more about the difference between NPTF & NPT.The profile properties, such as height, pitch, and truncations, are constant. However, the pitch diameter is not a constant value. It changes depending on the distance from the beginning of the thread. Because of that, the set of parameters and measuring techniques is very different (and often confusing) compared to Unified Inch and metric threads. To make the explanations and drawings more straightforward, we split them into 3 sections:An assembly drawing of an External and Internal thread showing only the parameters that are either common to both or are relevant to the assembly.External thread drawing with all its relevant dimensions.Internal thread drawing with all its relevant dimensions.Common Dimensions (External & Internal)When assembling with “hand force”, the male and female parts of a tapered thread will turn several rotations until the clearance is closed, and a “stop” is reached. This distance is called “Hand Tight Engagement Length”, and an “L1 Gauge usually measures it”. To form the seal, the assembly continues with a wrench an additional distance called “Wrench Allowance”.NPTF Pipe & Fitting Assembly DrawingSymbolsSymbolNameExplnationPpitchGiven in TPI, and used in calculations as distanceßThread Tapper AngleEquals 1°47' (1.7833°)Defined by ASME B1.20.3 as 0.0625 +/-0.0050 inch/inchαThread V half AngleEquals 30°Tolerance is defined in the below chartHHeight of the "sharp V"The height of the theoretical profile triangle.\( H=\frac{\sqrt{3}}{2}\times{P} \)hThread HeightDistance between the truncated root and crest. It is a result of the truncation tolerances as defined in the Below Chart.L1Length of hand-tight engagementThe maximum distance that the male and female parts can be threaded by normal hand force.E1Pitch diameter at the L1 PlaneThe Pitch d diameter at the plane of hand-tight engagement length (L1) of external thread (Pipe), and at the large end of internal thread (Fitting)L1 - L2Maximum Wrenching DistanceTo create a seal, the pipe and fitting should be further tightened by a wrench beyond the L1 plane.L3Minimum Wrenching DistanceNPTF External Thread DimensionsBasic DrawingProfile DrawingSymbolsSymbolNameExplnationP, H, h, L1, E1 α, and ß are defined in the assembly section above.DPipe ODOuter diameter of the pipeE0Pitch Diameter at the Pipe's endE0=D - (O.O5*D + 1.1 ) * PL2Length of Last usefull ThreadLength of Last proper Thread. At L2, the thread profile starts to get truncated, but it is still considered "useful" until this point.E2Pitch Diameter at E2 planeE2 = E0 + 0.0625 *  L2VLength of Vanish threadsThe length of "Unuseful" threads.Basic Dimensions Chart – NPTF External ThreadsDimensions are in Inches. To view metric values, click the Thread Description link.There are a total of 20 parameters for each thread size. The below charts show only the main ones. To view all the parameters, click the thread description link.ThreadPipepipe ODTPIPitchEnd Pitch Diameter (E0)Engagement Length (L1)1/16 - 27 NPTF1/160.3125270.03700.271180.160001/8 - 27 NPTF1/80.4050270.03700.363510.161501/4 - 18 NPTF1/40.5400180.05560.477390.227803/8 - 18 NPTF3/80.6750180.05560.612010.240001/2 - 14 NPTF1/20.8400140.07140.758430.320003/4 - 14 NPTF3/41.0500140.07140.967680.339001 - 11 1/2 NPTF11.3150120.08701.213630.400001 1/4 - 11 1/2 NPTF1 1/41.6600120.08701.557130.420001 1/2 - 11 1/2 NPTF1 1/21.9000120.08701.796090.420002 - 11 1/2 NPTF22.3750120.08702.269020.436002 1/2 - 8 NPTF2 1/22.875080.12502.719530.682003 - 8 NPTF33.500080.12503.340620.76600NPTF Internal Thread DimensionsBasic DrawingProfile DrawingSymbols for NPTF Internal (Fitting Thread)SymbolNameExplnationP, H, h, L1, E1 α, and ß are defined in the assembly section above.E1Large End Pitch DiameterE1 = E0 + 0.0625 *  L1E3Small End Pitch DiameterE3 = E1 - 0.0625 *  (L1+L3)L3Length of Wrenching AllowanceTo create a seal, the pipe and fitting should be tightened by a wrench beyond the L1 plane by a minimum distance of L3.L1 + L3Thread LengthMinimum Internal Thread lengthTTap Drill SizeRecomended Drill diameter for tapping.Basic Dimensions Chart – NPTF Internal ThreadsDimensions are in Inches. To view metric values, click the Thread Description Link.There are a total of 15 parameters for each thread size. The below charts show only the main ones. To view all the parameters, click the thread description link. ThreadTPIPitchEnd Pitch Diameter (E1)Min Thread LengthTap Drill Size1/16 - 27 NPTF270.03700.281180.271100.240501/8 - 27 NPTF270.03700.373600.272600.332301/4 - 18 NPTF180.05560.491630.394500.431503/8 - 18 NPTF180.05560.627010.406700.565901/2 - 14 NPTF140.07140.778430.534300.698303/4 - 14 NPTF140.07140.988870.553300.906701 - 11 1/2 NPTF120.08701.238630.660901.139001 1/4 - 11 1/2 NPTF120.08701.583380.680901.480501 1/2 - 11 1/2 NPTF120.08701.822340.680901.717502 - 11 1/2 NPTF120.08702.296270.696902.186402 1/2 - 8 NPTF80.12502.762161.057002.605403 - 8 NPTF80.12503.388501.141003.22450Limits & Tolerances for NPTF threadsThe tolerancing system for NPTF resembles the NPT standard’s requirements but is more strict in several respects:Taper angle tolerance.Truncation tolerances.Required gauging.Taper Angle (ß) ToleranceThe taper angle (Beta) is defined in ASME B1-20.3 as 0.0625 +/-0.0050 Inch per an inch length. If we measure the pitch diameter at a particular location, move one inch along the axis and measure it again, we should measure a difference in diameter of 0.0625″.I have no idea why an angle is defined in such a peculiar way; however, you can convert it to degrees using the below formula:\( \beta = 0.5 \times \tan^{-1} \left( { 0.0625 } \right) = 1.79^{\circ}\)The linear units are measured on the diameter, and the angle is measured “per side”. Therefore the 0.5 factor is applied.The tolerance field is about 60% compared to the field in regular NPT threads.Truncation and Height TolerancesDimensions are in Inches.The ASTM standard provides only the tolerance of the truncations.We calculated the height limits based on that.The tolerances depend only on the pitch.The tolerance field is about 60% compared to the field in regular NPT threads.TPIThread HeightCrest TruncationRoot TruncationHead Anglehminhmaxfminfmaxfminfmax2α (60°)270.023380.026880.00170.00350.00350.0052+/- 2.5°180.037710.041210.00260.00430.00430.0061+/- 2°140.05140.05490.00260.00430.00430.0061+/- 2°11.50.062310.066610.00350.00520.00520.0078+/- 1.5°80.091850.096150.00520.00690.00690.0095+/- 1.5°Gauging for acceptanceThe NPT standard requires only an L1 Gage.NPTF requires, in addition to the L1 gage, also: L2, L3, and “Crest Check” gages.NPSF – Nation Pipe Straight Fuel ThreadNPSF threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered NPTF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSF threads are used with ductile materials that can adjust at assembly to the external taper during assembly.They should not be used in hard/brittle materials.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSF Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2768 - 0.28030.24820.311/8" - 27 NPSF0.3692 - 0.37270.34060.311/4" - 18 NPSF0.4852 - 0.49040.44220.473/8" - 18 NPSF0.6205 - 0.62570.57760.51/2" - 14 NPSF0.77 - 0.77670.71330.663/4" - 14 NPSF0.9805 - 0.98720.92380.661" - 11 1/2 NPSF1.2284 - 1.23651.160.78Dimensions in InchesNPSI – Nation Pipe Straight Intermediate ThreadNPSI threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered PTF-SAE short threads.They have slightly larger diameters than the NPSF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSI threads are used with hard/brittle materials that can adjust at assembly to the external taper during assembly.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSI Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2791 - 0.28260.25050.311/8" - 27 NPSF0.3715 - 0.3750.34290.311/4" - 18 NPSF0.4886 - 0.49380.44570.473/8" - 18 NPSF0.624 - 0.62920.58110.51/2" - 14 NPSF0.7745 - 0.78120.7180.663/4" - 14 NPSF0.985 - 0.99170.92830.661" - 11 1/2 NPSF1.2338 - 1.2421.16550.78Dimensions in InchesPTF-SAE Short ThreadExternalPTF-SAE Short External threads conform in all parameters with NPTF external threads, except that the thread length is shorter by one thread from the small (entering) end. They are designed for applications with limited clearance.They are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT external threads are intended for assembly with NPSI or NPTF internal threads.InternalPTF-SAE Short Internal threads conform in all parameters with NPTF internal threads, except that the thread length is shorter by one thread from the large (entering) end. They are designed for thin materials where thickness is insufficient for the full thread length of NPTFThey are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT internal threads are intended for assembly with NPTF external threads.They cannot be assembled with PTF-SAE short external threads.Related Glossary Terms:PitchL1 GagePress FitLength of EngagementDuctilityMajor DiameterTooth per inch (tpi)Pitch DiameterThread Height (Depth)Thread TruncationTap Drill SizeMinor Diameter

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The taper angle (Beta) is defined in ASME B1-20.3 as 0.0625 +/-0.0050 Inch per an inch length. If we measure the pitch diameter at a particular location, move one inch along the axis and measure it again, we should measure a difference in diameter of 0.0625″.I have no idea why an angle is defined in such a peculiar way; however, you can convert it to degrees using the below formula:\( \beta = 0.5 \times \tan^{-1} \left( { 0.0625 } \right) = 1.79^{\circ}\)The linear units are measured on the diameter, and the angle is measured “per side”. Therefore the 0.5 factor is applied.The tolerance field is about 60% compared to the field in regular NPT threads.Truncation and Height TolerancesDimensions are in Inches.The ASTM standard provides only the tolerance of the truncations.We calculated the height limits based on that.The tolerances depend only on the pitch.The tolerance field is about 60% compared to the field in regular NPT threads.TPIThread HeightCrest TruncationRoot TruncationHead Anglehminhmaxfminfmaxfminfmax2α (60°)270.023380.026880.00170.00350.00350.0052+/- 2.5°180.037710.041210.00260.00430.00430.0061+/- 2°140.05140.05490.00260.00430.00430.0061+/- 2°11.50.062310.066610.00350.00520.00520.0078+/- 1.5°80.091850.096150.00520.00690.00690.0095+/- 1.5°Gauging for acceptanceThe NPT standard requires only an L1 Gage.NPTF requires, in addition to the L1 gage, also: L2, L3, and “Crest Check” gages.NPSF – Nation Pipe Straight Fuel ThreadNPSF threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered NPTF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSF threads are used with ductile materials that can adjust at assembly to the external taper during assembly.They should not be used in hard/brittle materials.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSF Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2768 - 0.28030.24820.311/8" - 27 NPSF0.3692 - 0.37270.34060.311/4" - 18 NPSF0.4852 - 0.49040.44220.473/8" - 18 NPSF0.6205 - 0.62570.57760.51/2" - 14 NPSF0.77 - 0.77670.71330.663/4" - 14 NPSF0.9805 - 0.98720.92380.661" - 11 1/2 NPSF1.2284 - 1.23651.160.78Dimensions in InchesNPSI – Nation Pipe Straight Intermediate ThreadNPSI threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered PTF-SAE short threads.They have slightly larger diameters than the NPSF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSI threads are used with hard/brittle materials that can adjust at assembly to the external taper during assembly.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSI Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2791 - 0.28260.25050.311/8" - 27 NPSF0.3715 - 0.3750.34290.311/4" - 18 NPSF0.4886 - 0.49380.44570.473/8" - 18 NPSF0.624 - 0.62920.58110.51/2" - 14 NPSF0.7745 - 0.78120.7180.663/4" - 14 NPSF0.985 - 0.99170.92830.661" - 11 1/2 NPSF1.2338 - 1.2421.16550.78Dimensions in InchesPTF-SAE Short ThreadExternalPTF-SAE Short External threads conform in all parameters with NPTF external threads, except that the thread length is shorter by one thread from the small (entering) end. They are designed for applications with limited clearance.They are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT external threads are intended for assembly with NPSI or NPTF internal threads.InternalPTF-SAE Short Internal threads conform in all parameters with NPTF internal threads, except that the thread length is shorter by one thread from the large (entering) end. They are designed for thin materials where thickness is insufficient for the full thread length of NPTFThey are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT internal threads are intended for assembly with NPTF external threads.They cannot be assembled with PTF-SAE short external threads.Related Glossary Terms:PitchL1 GagePress FitLength of EngagementDuctilityMajor DiameterTooth per inch (tpi)Pitch DiameterThread Height (Depth)Thread TruncationTap Drill SizeMinor Diameter

Selecting the right material for your drill bit isn’t just about the material you’re drilling; it’s also about the operation you’re performing.

There are several reasons so many of our customers like HSS drill bits. For one, it’s strong—HHS bits can handle a variety of metals without dulling quickly. Also, it can hold its temper under sweltering temperatures, which is necessary in metalworking. We cannot abandon the benefit of versatility. These bits are great for most general drilling tasks and can be used with various materials.

NPTF, PTF, NPSF, or NPSI. Where the meaning of each letter is:N = NationalP = PipeT = TaperS = StraightF = FuelI = IntermediateAdditional Parameters:Direction: By default, the thread is right-hand. For a left-hand thread, add the suffix -LH.NPTF series – National Pipe Taper Fuel ThreadNPTF stands for National Pipe Tapered Fuel. . The basic profile is identical to the common NPT thread. The main difference is that NPTF provides a leakproof seal without using a sealant. It is obtained by tight tolerances and gauging requirements that create interference fitting in all conditions. The thread profile is tapered at an angle of 1°47′ (0.0625 Inch per inch of length) relative to the axis. Learn more about the difference between NPTF & NPT.The profile properties, such as height, pitch, and truncations, are constant. However, the pitch diameter is not a constant value. It changes depending on the distance from the beginning of the thread. Because of that, the set of parameters and measuring techniques is very different (and often confusing) compared to Unified Inch and metric threads. To make the explanations and drawings more straightforward, we split them into 3 sections:An assembly drawing of an External and Internal thread showing only the parameters that are either common to both or are relevant to the assembly.External thread drawing with all its relevant dimensions.Internal thread drawing with all its relevant dimensions.Common Dimensions (External & Internal)When assembling with “hand force”, the male and female parts of a tapered thread will turn several rotations until the clearance is closed, and a “stop” is reached. This distance is called “Hand Tight Engagement Length”, and an “L1 Gauge usually measures it”. To form the seal, the assembly continues with a wrench an additional distance called “Wrench Allowance”.NPTF Pipe & Fitting Assembly DrawingSymbolsSymbolNameExplnationPpitchGiven in TPI, and used in calculations as distanceßThread Tapper AngleEquals 1°47' (1.7833°)Defined by ASME B1.20.3 as 0.0625 +/-0.0050 inch/inchαThread V half AngleEquals 30°Tolerance is defined in the below chartHHeight of the "sharp V"The height of the theoretical profile triangle.\( H=\frac{\sqrt{3}}{2}\times{P} \)hThread HeightDistance between the truncated root and crest. It is a result of the truncation tolerances as defined in the Below Chart.L1Length of hand-tight engagementThe maximum distance that the male and female parts can be threaded by normal hand force.E1Pitch diameter at the L1 PlaneThe Pitch d diameter at the plane of hand-tight engagement length (L1) of external thread (Pipe), and at the large end of internal thread (Fitting)L1 - L2Maximum Wrenching DistanceTo create a seal, the pipe and fitting should be further tightened by a wrench beyond the L1 plane.L3Minimum Wrenching DistanceNPTF External Thread DimensionsBasic DrawingProfile DrawingSymbolsSymbolNameExplnationP, H, h, L1, E1 α, and ß are defined in the assembly section above.DPipe ODOuter diameter of the pipeE0Pitch Diameter at the Pipe's endE0=D - (O.O5*D + 1.1 ) * PL2Length of Last usefull ThreadLength of Last proper Thread. At L2, the thread profile starts to get truncated, but it is still considered "useful" until this point.E2Pitch Diameter at E2 planeE2 = E0 + 0.0625 *  L2VLength of Vanish threadsThe length of "Unuseful" threads.Basic Dimensions Chart – NPTF External ThreadsDimensions are in Inches. To view metric values, click the Thread Description link.There are a total of 20 parameters for each thread size. The below charts show only the main ones. To view all the parameters, click the thread description link.ThreadPipepipe ODTPIPitchEnd Pitch Diameter (E0)Engagement Length (L1)1/16 - 27 NPTF1/160.3125270.03700.271180.160001/8 - 27 NPTF1/80.4050270.03700.363510.161501/4 - 18 NPTF1/40.5400180.05560.477390.227803/8 - 18 NPTF3/80.6750180.05560.612010.240001/2 - 14 NPTF1/20.8400140.07140.758430.320003/4 - 14 NPTF3/41.0500140.07140.967680.339001 - 11 1/2 NPTF11.3150120.08701.213630.400001 1/4 - 11 1/2 NPTF1 1/41.6600120.08701.557130.420001 1/2 - 11 1/2 NPTF1 1/21.9000120.08701.796090.420002 - 11 1/2 NPTF22.3750120.08702.269020.436002 1/2 - 8 NPTF2 1/22.875080.12502.719530.682003 - 8 NPTF33.500080.12503.340620.76600NPTF Internal Thread DimensionsBasic DrawingProfile DrawingSymbols for NPTF Internal (Fitting Thread)SymbolNameExplnationP, H, h, L1, E1 α, and ß are defined in the assembly section above.E1Large End Pitch DiameterE1 = E0 + 0.0625 *  L1E3Small End Pitch DiameterE3 = E1 - 0.0625 *  (L1+L3)L3Length of Wrenching AllowanceTo create a seal, the pipe and fitting should be tightened by a wrench beyond the L1 plane by a minimum distance of L3.L1 + L3Thread LengthMinimum Internal Thread lengthTTap Drill SizeRecomended Drill diameter for tapping.Basic Dimensions Chart – NPTF Internal ThreadsDimensions are in Inches. To view metric values, click the Thread Description Link.There are a total of 15 parameters for each thread size. The below charts show only the main ones. To view all the parameters, click the thread description link. ThreadTPIPitchEnd Pitch Diameter (E1)Min Thread LengthTap Drill Size1/16 - 27 NPTF270.03700.281180.271100.240501/8 - 27 NPTF270.03700.373600.272600.332301/4 - 18 NPTF180.05560.491630.394500.431503/8 - 18 NPTF180.05560.627010.406700.565901/2 - 14 NPTF140.07140.778430.534300.698303/4 - 14 NPTF140.07140.988870.553300.906701 - 11 1/2 NPTF120.08701.238630.660901.139001 1/4 - 11 1/2 NPTF120.08701.583380.680901.480501 1/2 - 11 1/2 NPTF120.08701.822340.680901.717502 - 11 1/2 NPTF120.08702.296270.696902.186402 1/2 - 8 NPTF80.12502.762161.057002.605403 - 8 NPTF80.12503.388501.141003.22450Limits & Tolerances for NPTF threadsThe tolerancing system for NPTF resembles the NPT standard’s requirements but is more strict in several respects:Taper angle tolerance.Truncation tolerances.Required gauging.Taper Angle (ß) ToleranceThe taper angle (Beta) is defined in ASME B1-20.3 as 0.0625 +/-0.0050 Inch per an inch length. If we measure the pitch diameter at a particular location, move one inch along the axis and measure it again, we should measure a difference in diameter of 0.0625″.I have no idea why an angle is defined in such a peculiar way; however, you can convert it to degrees using the below formula:\( \beta = 0.5 \times \tan^{-1} \left( { 0.0625 } \right) = 1.79^{\circ}\)The linear units are measured on the diameter, and the angle is measured “per side”. Therefore the 0.5 factor is applied.The tolerance field is about 60% compared to the field in regular NPT threads.Truncation and Height TolerancesDimensions are in Inches.The ASTM standard provides only the tolerance of the truncations.We calculated the height limits based on that.The tolerances depend only on the pitch.The tolerance field is about 60% compared to the field in regular NPT threads.TPIThread HeightCrest TruncationRoot TruncationHead Anglehminhmaxfminfmaxfminfmax2α (60°)270.023380.026880.00170.00350.00350.0052+/- 2.5°180.037710.041210.00260.00430.00430.0061+/- 2°140.05140.05490.00260.00430.00430.0061+/- 2°11.50.062310.066610.00350.00520.00520.0078+/- 1.5°80.091850.096150.00520.00690.00690.0095+/- 1.5°Gauging for acceptanceThe NPT standard requires only an L1 Gage.NPTF requires, in addition to the L1 gage, also: L2, L3, and “Crest Check” gages.NPSF – Nation Pipe Straight Fuel ThreadNPSF threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered NPTF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSF threads are used with ductile materials that can adjust at assembly to the external taper during assembly.They should not be used in hard/brittle materials.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSF Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2768 - 0.28030.24820.311/8" - 27 NPSF0.3692 - 0.37270.34060.311/4" - 18 NPSF0.4852 - 0.49040.44220.473/8" - 18 NPSF0.6205 - 0.62570.57760.51/2" - 14 NPSF0.77 - 0.77670.71330.663/4" - 14 NPSF0.9805 - 0.98720.92380.661" - 11 1/2 NPSF1.2284 - 1.23651.160.78Dimensions in InchesNPSI – Nation Pipe Straight Intermediate ThreadNPSI threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered PTF-SAE short threads.They have slightly larger diameters than the NPSF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSI threads are used with hard/brittle materials that can adjust at assembly to the external taper during assembly.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSI Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2791 - 0.28260.25050.311/8" - 27 NPSF0.3715 - 0.3750.34290.311/4" - 18 NPSF0.4886 - 0.49380.44570.473/8" - 18 NPSF0.624 - 0.62920.58110.51/2" - 14 NPSF0.7745 - 0.78120.7180.663/4" - 14 NPSF0.985 - 0.99170.92830.661" - 11 1/2 NPSF1.2338 - 1.2421.16550.78Dimensions in InchesPTF-SAE Short ThreadExternalPTF-SAE Short External threads conform in all parameters with NPTF external threads, except that the thread length is shorter by one thread from the small (entering) end. They are designed for applications with limited clearance.They are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT external threads are intended for assembly with NPSI or NPTF internal threads.InternalPTF-SAE Short Internal threads conform in all parameters with NPTF internal threads, except that the thread length is shorter by one thread from the large (entering) end. They are designed for thin materials where thickness is insufficient for the full thread length of NPTFThey are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT internal threads are intended for assembly with NPTF external threads.They cannot be assembled with PTF-SAE short external threads.Related Glossary Terms:PitchL1 GagePress FitLength of EngagementDuctilityMajor DiameterTooth per inch (tpi)Pitch DiameterThread Height (Depth)Thread TruncationTap Drill SizeMinor Diameter

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NPTFthread dimensions pdf

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Because of that, the set of parameters and measuring techniques is very different (and often confusing) compared to Unified Inch and metric threads. To make the explanations and drawings more straightforward, we split them into 3 sections:An assembly drawing of an External and Internal thread showing only the parameters that are either common to both or are relevant to the assembly.External thread drawing with all its relevant dimensions.Internal thread drawing with all its relevant dimensions.Common Dimensions (External & Internal)When assembling with “hand force”, the male and female parts of a tapered thread will turn several rotations until the clearance is closed, and a “stop” is reached. This distance is called “Hand Tight Engagement Length”, and an “L1 Gauge usually measures it”. To form the seal, the assembly continues with a wrench an additional distance called “Wrench Allowance”.NPTF Pipe & Fitting Assembly DrawingSymbolsSymbolNameExplnationPpitchGiven in TPI, and used in calculations as distanceßThread Tapper AngleEquals 1°47' (1.7833°)Defined by ASME B1.20.3 as 0.0625 +/-0.0050 inch/inchαThread V half AngleEquals 30°Tolerance is defined in the below chartHHeight of the "sharp V"The height of the theoretical profile triangle.\( H=\frac{\sqrt{3}}{2}\times{P} \)hThread HeightDistance between the truncated root and crest. It is a result of the truncation tolerances as defined in the Below Chart.L1Length of hand-tight engagementThe maximum distance that the male and female parts can be threaded by normal hand force.E1Pitch diameter at the L1 PlaneThe Pitch d diameter at the plane of hand-tight engagement length (L1) of external thread (Pipe), and at the large end of internal thread (Fitting)L1 - L2Maximum Wrenching DistanceTo create a seal, the pipe and fitting should be further tightened by a wrench beyond the L1 plane.L3Minimum Wrenching DistanceNPTF External Thread DimensionsBasic DrawingProfile DrawingSymbolsSymbolNameExplnationP, H, h, L1, E1 α, and ß are defined in the assembly section above.DPipe ODOuter diameter of the pipeE0Pitch Diameter at the Pipe's endE0=D - (O.O5*D + 1.1 ) * PL2Length of Last usefull ThreadLength of Last proper Thread. At L2, the thread profile starts to get truncated, but it is still considered "useful" until this point.E2Pitch Diameter at E2 planeE2 = E0 + 0.0625 *  L2VLength of Vanish threadsThe length of "Unuseful" threads.Basic Dimensions Chart – NPTF External ThreadsDimensions are in Inches. To view metric values, click the Thread Description link.There are a total of 20 parameters for each thread size. The below charts show only the main ones. To view all the parameters, click the thread description link.ThreadPipepipe ODTPIPitchEnd Pitch Diameter (E0)Engagement Length (L1)1/16 - 27 NPTF1/160.3125270.03700.271180.160001/8 - 27 NPTF1/80.4050270.03700.363510.161501/4 - 18 NPTF1/40.5400180.05560.477390.227803/8 - 18 NPTF3/80.6750180.05560.612010.240001/2 - 14 NPTF1/20.8400140.07140.758430.320003/4 - 14 NPTF3/41.0500140.07140.967680.339001 - 11 1/2 NPTF11.3150120.08701.213630.400001 1/4 - 11 1/2 NPTF1 1/41.6600120.08701.557130.420001 1/2 - 11 1/2 NPTF1 1/21.9000120.08701.796090.420002 - 11 1/2 NPTF22.3750120.08702.269020.436002 1/2 - 8 NPTF2 1/22.875080.12502.719530.682003 - 8 NPTF33.500080.12503.340620.76600NPTF Internal Thread DimensionsBasic DrawingProfile DrawingSymbols for NPTF Internal (Fitting Thread)SymbolNameExplnationP, H, h, L1, E1 α, and ß are defined in the assembly section above.E1Large End Pitch DiameterE1 = E0 + 0.0625 *  L1E3Small End Pitch DiameterE3 = E1 - 0.0625 *  (L1+L3)L3Length of Wrenching AllowanceTo create a seal, the pipe and fitting should be tightened by a wrench beyond the L1 plane by a minimum distance of L3.L1 + L3Thread LengthMinimum Internal Thread lengthTTap Drill SizeRecomended Drill diameter for tapping.Basic Dimensions Chart – NPTF Internal ThreadsDimensions are in Inches. To view metric values, click the Thread Description Link.There are a total of 15 parameters for each thread size. The below charts show only the main ones. To view all the parameters, click the thread description link. ThreadTPIPitchEnd Pitch Diameter (E1)Min Thread LengthTap Drill Size1/16 - 27 NPTF270.03700.281180.271100.240501/8 - 27 NPTF270.03700.373600.272600.332301/4 - 18 NPTF180.05560.491630.394500.431503/8 - 18 NPTF180.05560.627010.406700.565901/2 - 14 NPTF140.07140.778430.534300.698303/4 - 14 NPTF140.07140.988870.553300.906701 - 11 1/2 NPTF120.08701.238630.660901.139001 1/4 - 11 1/2 NPTF120.08701.583380.680901.480501 1/2 - 11 1/2 NPTF120.08701.822340.680901.717502 - 11 1/2 NPTF120.08702.296270.696902.186402 1/2 - 8 NPTF80.12502.762161.057002.605403 - 8 NPTF80.12503.388501.141003.22450Limits & Tolerances for NPTF threadsThe tolerancing system for NPTF resembles the NPT standard’s requirements but is more strict in several respects:Taper angle tolerance.Truncation tolerances.Required gauging.Taper Angle (ß) ToleranceThe taper angle (Beta) is defined in ASME B1-20.3 as 0.0625 +/-0.0050 Inch per an inch length. If we measure the pitch diameter at a particular location, move one inch along the axis and measure it again, we should measure a difference in diameter of 0.0625″.I have no idea why an angle is defined in such a peculiar way; however, you can convert it to degrees using the below formula:\( \beta = 0.5 \times \tan^{-1} \left( { 0.0625 } \right) = 1.79^{\circ}\)The linear units are measured on the diameter, and the angle is measured “per side”. Therefore the 0.5 factor is applied.The tolerance field is about 60% compared to the field in regular NPT threads.Truncation and Height TolerancesDimensions are in Inches.The ASTM standard provides only the tolerance of the truncations.We calculated the height limits based on that.The tolerances depend only on the pitch.The tolerance field is about 60% compared to the field in regular NPT threads.TPIThread HeightCrest TruncationRoot TruncationHead Anglehminhmaxfminfmaxfminfmax2α (60°)270.023380.026880.00170.00350.00350.0052+/- 2.5°180.037710.041210.00260.00430.00430.0061+/- 2°140.05140.05490.00260.00430.00430.0061+/- 2°11.50.062310.066610.00350.00520.00520.0078+/- 1.5°80.091850.096150.00520.00690.00690.0095+/- 1.5°Gauging for acceptanceThe NPT standard requires only an L1 Gage.NPTF requires, in addition to the L1 gage, also: L2, L3, and “Crest Check” gages.NPSF – Nation Pipe Straight Fuel ThreadNPSF threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered NPTF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSF threads are used with ductile materials that can adjust at assembly to the external taper during assembly.They should not be used in hard/brittle materials.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSF Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2768 - 0.28030.24820.311/8" - 27 NPSF0.3692 - 0.37270.34060.311/4" - 18 NPSF0.4852 - 0.49040.44220.473/8" - 18 NPSF0.6205 - 0.62570.57760.51/2" - 14 NPSF0.77 - 0.77670.71330.663/4" - 14 NPSF0.9805 - 0.98720.92380.661" - 11 1/2 NPSF1.2284 - 1.23651.160.78Dimensions in InchesNPSI – Nation Pipe Straight Intermediate ThreadNPSI threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered PTF-SAE short threads.They have slightly larger diameters than the NPSF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSI threads are used with hard/brittle materials that can adjust at assembly to the external taper during assembly.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSI Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2791 - 0.28260.25050.311/8" - 27 NPSF0.3715 - 0.3750.34290.311/4" - 18 NPSF0.4886 - 0.49380.44570.473/8" - 18 NPSF0.624 - 0.62920.58110.51/2" - 14 NPSF0.7745 - 0.78120.7180.663/4" - 14 NPSF0.985 - 0.99170.92830.661" - 11 1/2 NPSF1.2338 - 1.2421.16550.78Dimensions in InchesPTF-SAE Short ThreadExternalPTF-SAE Short External threads conform in all parameters with NPTF external threads, except that the thread length is shorter by one thread from the small (entering) end. They are designed for applications with limited clearance.They are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT external threads are intended for assembly with NPSI or NPTF internal threads.InternalPTF-SAE Short Internal threads conform in all parameters with NPTF internal threads, except that the thread length is shorter by one thread from the large (entering) end. They are designed for thin materials where thickness is insufficient for the full thread length of NPTFThey are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT internal threads are intended for assembly with NPTF external threads.They cannot be assembled with PTF-SAE short external threads.Related Glossary Terms:PitchL1 GagePress FitLength of EngagementDuctilityMajor DiameterTooth per inch (tpi)Pitch DiameterThread Height (Depth)Thread TruncationTap Drill SizeMinor Diameter

Most of the dimensions of NPTF threads are identical to NPT. The main difference are the tolerance requirements which are more strict for NPTF.Mating and Truncation TolerancesWhen internal and external pipe threads are tightened, one of three mating conditions can occur: Clear, Contact, or interference.NPTFNPTSeparate truncation tolerance for root and crestThe root and the crest share the sane toleranceTight truncation tolerance field of about 2%-4% of the pitch.Truncation tolerance is about 3%-6% of the pitch* LMC creates contact between the root and the crest.* MMC creates interference between the root and the crest..Mating crests and roots may clear, contact, or interfere. The thread may not necessarily seal unless a sealant is used.Taper Angle ToleranceThe nominal taper angle is 1.709° for both standards. However, the tolerance field in NPTF is 0.3°, and NPT 0.5°. The outcome of both the taper and the truncation having tighter control leads to higher repeatability of sealing performance when using NPTF threads.Gauging for acceptanceThe NPT standard requires only an L1 Gage.NPTF requires, in addition to the L1 gage, also: L2, L3, and “Crest Check” gages.Production CostMachining: The production process for NTF and NPT is the same. Therefore the machining cost is identical.Inspection: The NPTF standard requires 3 gaging tests for acceptance (Only one in NPT). Therefore the inspection cost of NPTF is higher.Quality: The scrap rate in the production of NPTF threads is higher. An unattentive worker can easily produce nonconforming parts. This is the most significant factor that increases the cost of NPTF threads.Sealing PerformanceNPTF root and crest truncation tolerances are adjusted for an interference fit which creates a mechanical seal through thread form deformation at assembly. There is no need for PTFE, Teflon tapes, or any other sealant.NPT needs a sealant to be leak-free. A sealing material such as PTFE or Teflon must be used to prevent leaks.When is it necessary to use a mechanical seal?Using sealants could contaminate the fluids or gasses flowing through the system.A sealant might fail because of high heat or high pressure.List of Series defined in ASME B1-20.3NameDescriptionNPTFNational Pipe Taper FuelThe primary series for all service conditions.PTF-SAE ShortShort Pipe Tapar FuelSaves raw material where a full thread engagement length is not criticalNPSFNational Pipe Straight FuelInternal only straight thread for ductile materialsNPSINational Pipe Straight IntermediateInternal only straight thread for hard materialsDesignations of Dryseal Pipe ThreadsBasic designation syntax:Nominal Diameter in Inch FractionPitch in TPISeries: NPTF / PTF-SAE / NPSF / NPSI.DirectionDiameter:The diameters are given in inch fractions. For example, 1/4″, 3/4″, and 1 1/4″.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″).It is also allowed to denote the pitch by distance. For example, 1/4-0.05P means a thread with a pitch of 0.05″ (same as 20 TPI).Series:NPTF, PTF, NPSF, or NPSI. Where the meaning of each letter is:N = NationalP = PipeT = TaperS = StraightF = FuelI = IntermediateAdditional Parameters:Direction: By default, the thread is right-hand. For a left-hand thread, add the suffix -LH.NPTF series – National Pipe Taper Fuel ThreadNPTF stands for National Pipe Tapered Fuel. . The basic profile is identical to the common NPT thread. The main difference is that NPTF provides a leakproof seal without using a sealant. It is obtained by tight tolerances and gauging requirements that create interference fitting in all conditions. The thread profile is tapered at an angle of 1°47′ (0.0625 Inch per inch of length) relative to the axis. Learn more about the difference between NPTF & NPT.The profile properties, such as height, pitch, and truncations, are constant. However, the pitch diameter is not a constant value. It changes depending on the distance from the beginning of the thread. Because of that, the set of parameters and measuring techniques is very different (and often confusing) compared to Unified Inch and metric threads. To make the explanations and drawings more straightforward, we split them into 3 sections:An assembly drawing of an External and Internal thread showing only the parameters that are either common to both or are relevant to the assembly.External thread drawing with all its relevant dimensions.Internal thread drawing with all its relevant dimensions.Common Dimensions (External & Internal)When assembling with “hand force”, the male and female parts of a tapered thread will turn several rotations until the clearance is closed, and a “stop” is reached. This distance is called “Hand Tight Engagement Length”, and an “L1 Gauge usually measures it”. To form the seal, the assembly continues with a wrench an additional distance called “Wrench Allowance”.NPTF Pipe & Fitting Assembly DrawingSymbolsSymbolNameExplnationPpitchGiven in TPI, and used in calculations as distanceßThread Tapper AngleEquals 1°47' (1.7833°)Defined by ASME B1.20.3 as 0.0625 +/-0.0050 inch/inchαThread V half AngleEquals 30°Tolerance is defined in the below chartHHeight of the "sharp V"The height of the theoretical profile triangle.\( H=\frac{\sqrt{3}}{2}\times{P} \)hThread HeightDistance between the truncated root and crest. It is a result of the truncation tolerances as defined in the Below Chart.L1Length of hand-tight engagementThe maximum distance that the male and female parts can be threaded by normal hand force.E1Pitch diameter at the L1 PlaneThe Pitch d diameter at the plane of hand-tight engagement length (L1) of external thread (Pipe), and at the large end of internal thread (Fitting)L1 - L2Maximum Wrenching DistanceTo create a seal, the pipe and fitting should be further tightened by a wrench beyond the L1 plane.L3Minimum Wrenching DistanceNPTF External Thread DimensionsBasic DrawingProfile DrawingSymbolsSymbolNameExplnationP, H, h, L1, E1 α, and ß are defined in the assembly section above.DPipe ODOuter diameter of the pipeE0Pitch Diameter at the Pipe's endE0=D - (O.O5*D + 1.1 ) * PL2Length of Last usefull ThreadLength of Last proper Thread. At L2, the thread profile starts to get truncated, but it is still considered "useful" until this point.E2Pitch Diameter at E2 planeE2 = E0 + 0.0625 *  L2VLength of Vanish threadsThe length of "Unuseful" threads.Basic Dimensions Chart – NPTF External ThreadsDimensions are in Inches. To view metric values, click the Thread Description link.There are a total of 20 parameters for each thread size. The below charts show only the main ones. To view all the parameters, click the thread description link.ThreadPipepipe ODTPIPitchEnd Pitch Diameter (E0)Engagement Length (L1)1/16 - 27 NPTF1/160.3125270.03700.271180.160001/8 - 27 NPTF1/80.4050270.03700.363510.161501/4 - 18 NPTF1/40.5400180.05560.477390.227803/8 - 18 NPTF3/80.6750180.05560.612010.240001/2 - 14 NPTF1/20.8400140.07140.758430.320003/4 - 14 NPTF3/41.0500140.07140.967680.339001 - 11 1/2 NPTF11.3150120.08701.213630.400001 1/4 - 11 1/2 NPTF1 1/41.6600120.08701.557130.420001 1/2 - 11 1/2 NPTF1 1/21.9000120.08701.796090.420002 - 11 1/2 NPTF22.3750120.08702.269020.436002 1/2 - 8 NPTF2 1/22.875080.12502.719530.682003 - 8 NPTF33.500080.12503.340620.76600NPTF Internal Thread DimensionsBasic DrawingProfile DrawingSymbols for NPTF Internal (Fitting Thread)SymbolNameExplnationP, H, h, L1, E1 α, and ß are defined in the assembly section above.E1Large End Pitch DiameterE1 = E0 + 0.0625 *  L1E3Small End Pitch DiameterE3 = E1 - 0.0625 *  (L1+L3)L3Length of Wrenching AllowanceTo create a seal, the pipe and fitting should be tightened by a wrench beyond the L1 plane by a minimum distance of L3.L1 + L3Thread LengthMinimum Internal Thread lengthTTap Drill SizeRecomended Drill diameter for tapping.Basic Dimensions Chart – NPTF Internal ThreadsDimensions are in Inches. To view metric values, click the Thread Description Link.There are a total of 15 parameters for each thread size. The below charts show only the main ones. To view all the parameters, click the thread description link. ThreadTPIPitchEnd Pitch Diameter (E1)Min Thread LengthTap Drill Size1/16 - 27 NPTF270.03700.281180.271100.240501/8 - 27 NPTF270.03700.373600.272600.332301/4 - 18 NPTF180.05560.491630.394500.431503/8 - 18 NPTF180.05560.627010.406700.565901/2 - 14 NPTF140.07140.778430.534300.698303/4 - 14 NPTF140.07140.988870.553300.906701 - 11 1/2 NPTF120.08701.238630.660901.139001 1/4 - 11 1/2 NPTF120.08701.583380.680901.480501 1/2 - 11 1/2 NPTF120.08701.822340.680901.717502 - 11 1/2 NPTF120.08702.296270.696902.186402 1/2 - 8 NPTF80.12502.762161.057002.605403 - 8 NPTF80.12503.388501.141003.22450Limits & Tolerances for NPTF threadsThe tolerancing system for NPTF resembles the NPT standard’s requirements but is more strict in several respects:Taper angle tolerance.Truncation tolerances.Required gauging.Taper Angle (ß) ToleranceThe taper angle (Beta) is defined in ASME B1-20.3 as 0.0625 +/-0.0050 Inch per an inch length. If we measure the pitch diameter at a particular location, move one inch along the axis and measure it again, we should measure a difference in diameter of 0.0625″.I have no idea why an angle is defined in such a peculiar way; however, you can convert it to degrees using the below formula:\( \beta = 0.5 \times \tan^{-1} \left( { 0.0625 } \right) = 1.79^{\circ}\)The linear units are measured on the diameter, and the angle is measured “per side”. Therefore the 0.5 factor is applied.The tolerance field is about 60% compared to the field in regular NPT threads.Truncation and Height TolerancesDimensions are in Inches.The ASTM standard provides only the tolerance of the truncations.We calculated the height limits based on that.The tolerances depend only on the pitch.The tolerance field is about 60% compared to the field in regular NPT threads.TPIThread HeightCrest TruncationRoot TruncationHead Anglehminhmaxfminfmaxfminfmax2α (60°)270.023380.026880.00170.00350.00350.0052+/- 2.5°180.037710.041210.00260.00430.00430.0061+/- 2°140.05140.05490.00260.00430.00430.0061+/- 2°11.50.062310.066610.00350.00520.00520.0078+/- 1.5°80.091850.096150.00520.00690.00690.0095+/- 1.5°Gauging for acceptanceThe NPT standard requires only an L1 Gage.NPTF requires, in addition to the L1 gage, also: L2, L3, and “Crest Check” gages.NPSF – Nation Pipe Straight Fuel ThreadNPSF threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered NPTF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSF threads are used with ductile materials that can adjust at assembly to the external taper during assembly.They should not be used in hard/brittle materials.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSF Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2768 - 0.28030.24820.311/8" - 27 NPSF0.3692 - 0.37270.34060.311/4" - 18 NPSF0.4852 - 0.49040.44220.473/8" - 18 NPSF0.6205 - 0.62570.57760.51/2" - 14 NPSF0.77 - 0.77670.71330.663/4" - 14 NPSF0.9805 - 0.98720.92380.661" - 11 1/2 NPSF1.2284 - 1.23651.160.78Dimensions in InchesNPSI – Nation Pipe Straight Intermediate ThreadNPSI threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered PTF-SAE short threads.They have slightly larger diameters than the NPSF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSI threads are used with hard/brittle materials that can adjust at assembly to the external taper during assembly.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSI Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2791 - 0.28260.25050.311/8" - 27 NPSF0.3715 - 0.3750.34290.311/4" - 18 NPSF0.4886 - 0.49380.44570.473/8" - 18 NPSF0.624 - 0.62920.58110.51/2" - 14 NPSF0.7745 - 0.78120.7180.663/4" - 14 NPSF0.985 - 0.99170.92830.661" - 11 1/2 NPSF1.2338 - 1.2421.16550.78Dimensions in InchesPTF-SAE Short ThreadExternalPTF-SAE Short External threads conform in all parameters with NPTF external threads, except that the thread length is shorter by one thread from the small (entering) end. They are designed for applications with limited clearance.They are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT external threads are intended for assembly with NPSI or NPTF internal threads.InternalPTF-SAE Short Internal threads conform in all parameters with NPTF internal threads, except that the thread length is shorter by one thread from the large (entering) end. They are designed for thin materials where thickness is insufficient for the full thread length of NPTFThey are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT internal threads are intended for assembly with NPTF external threads.They cannot be assembled with PTF-SAE short external threads.Related Glossary Terms:PitchL1 GagePress FitLength of EngagementDuctilityMajor DiameterTooth per inch (tpi)Pitch DiameterThread Height (Depth)Thread TruncationTap Drill SizeMinor Diameter

Table of ContentsNPTF Vs. NPTTolerancing and AcceptanceProduction CostSealing PerformanceList of Series defined in ASME B1-20.3DesignationsNPTF series – National Pipe Taper Fuel ThreadCommon Dimensions (External & Internal)External Thread DimensionsInternal Thread DimensionsLimits & TolerancesNPSF – Nation Pipe Straight Fuel ThreadNPSI – Nation Pipe Straight Intermediate ThreadPTF-SAE Short Thread

Precision and cleanliness of cuts are paramount for woodworking, which is why brad-point bits with a sharp center point and two spurs are popular. They often come in HSS or high-carbon steel and are perfect for drilling clean interior holes without splintering the wood.

When internal and external pipe threads are tightened, one of three mating conditions can occur: Clear, Contact, or interference.NPTFNPTSeparate truncation tolerance for root and crestThe root and the crest share the sane toleranceTight truncation tolerance field of about 2%-4% of the pitch.Truncation tolerance is about 3%-6% of the pitch* LMC creates contact between the root and the crest.* MMC creates interference between the root and the crest..Mating crests and roots may clear, contact, or interfere. The thread may not necessarily seal unless a sealant is used.Taper Angle ToleranceThe nominal taper angle is 1.709° for both standards. However, the tolerance field in NPTF is 0.3°, and NPT 0.5°. The outcome of both the taper and the truncation having tighter control leads to higher repeatability of sealing performance when using NPTF threads.Gauging for acceptanceThe NPT standard requires only an L1 Gage.NPTF requires, in addition to the L1 gage, also: L2, L3, and “Crest Check” gages.Production CostMachining: The production process for NTF and NPT is the same. Therefore the machining cost is identical.Inspection: The NPTF standard requires 3 gaging tests for acceptance (Only one in NPT). Therefore the inspection cost of NPTF is higher.Quality: The scrap rate in the production of NPTF threads is higher. An unattentive worker can easily produce nonconforming parts. This is the most significant factor that increases the cost of NPTF threads.Sealing PerformanceNPTF root and crest truncation tolerances are adjusted for an interference fit which creates a mechanical seal through thread form deformation at assembly. There is no need for PTFE, Teflon tapes, or any other sealant.NPT needs a sealant to be leak-free. A sealing material such as PTFE or Teflon must be used to prevent leaks.When is it necessary to use a mechanical seal?Using sealants could contaminate the fluids or gasses flowing through the system.A sealant might fail because of high heat or high pressure.List of Series defined in ASME B1-20.3NameDescriptionNPTFNational Pipe Taper FuelThe primary series for all service conditions.PTF-SAE ShortShort Pipe Tapar FuelSaves raw material where a full thread engagement length is not criticalNPSFNational Pipe Straight FuelInternal only straight thread for ductile materialsNPSINational Pipe Straight IntermediateInternal only straight thread for hard materialsDesignations of Dryseal Pipe ThreadsBasic designation syntax:Nominal Diameter in Inch FractionPitch in TPISeries: NPTF / PTF-SAE / NPSF / NPSI.DirectionDiameter:The diameters are given in inch fractions. For example, 1/4″, 3/4″, and 1 1/4″.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″).It is also allowed to denote the pitch by distance. For example, 1/4-0.05P means a thread with a pitch of 0.05″ (same as 20 TPI).Series:NPTF, PTF, NPSF, or NPSI. Where the meaning of each letter is:N = NationalP = PipeT = TaperS = StraightF = FuelI = IntermediateAdditional Parameters:Direction: By default, the thread is right-hand. For a left-hand thread, add the suffix -LH.NPTF series – National Pipe Taper Fuel ThreadNPTF stands for National Pipe Tapered Fuel. . The basic profile is identical to the common NPT thread. The main difference is that NPTF provides a leakproof seal without using a sealant. It is obtained by tight tolerances and gauging requirements that create interference fitting in all conditions. The thread profile is tapered at an angle of 1°47′ (0.0625 Inch per inch of length) relative to the axis. Learn more about the difference between NPTF & NPT.The profile properties, such as height, pitch, and truncations, are constant. However, the pitch diameter is not a constant value. It changes depending on the distance from the beginning of the thread. Because of that, the set of parameters and measuring techniques is very different (and often confusing) compared to Unified Inch and metric threads. To make the explanations and drawings more straightforward, we split them into 3 sections:An assembly drawing of an External and Internal thread showing only the parameters that are either common to both or are relevant to the assembly.External thread drawing with all its relevant dimensions.Internal thread drawing with all its relevant dimensions.Common Dimensions (External & Internal)When assembling with “hand force”, the male and female parts of a tapered thread will turn several rotations until the clearance is closed, and a “stop” is reached. This distance is called “Hand Tight Engagement Length”, and an “L1 Gauge usually measures it”. To form the seal, the assembly continues with a wrench an additional distance called “Wrench Allowance”.NPTF Pipe & Fitting Assembly DrawingSymbolsSymbolNameExplnationPpitchGiven in TPI, and used in calculations as distanceßThread Tapper AngleEquals 1°47' (1.7833°)Defined by ASME B1.20.3 as 0.0625 +/-0.0050 inch/inchαThread V half AngleEquals 30°Tolerance is defined in the below chartHHeight of the "sharp V"The height of the theoretical profile triangle.\( H=\frac{\sqrt{3}}{2}\times{P} \)hThread HeightDistance between the truncated root and crest. It is a result of the truncation tolerances as defined in the Below Chart.L1Length of hand-tight engagementThe maximum distance that the male and female parts can be threaded by normal hand force.E1Pitch diameter at the L1 PlaneThe Pitch d diameter at the plane of hand-tight engagement length (L1) of external thread (Pipe), and at the large end of internal thread (Fitting)L1 - L2Maximum Wrenching DistanceTo create a seal, the pipe and fitting should be further tightened by a wrench beyond the L1 plane.L3Minimum Wrenching DistanceNPTF External Thread DimensionsBasic DrawingProfile DrawingSymbolsSymbolNameExplnationP, H, h, L1, E1 α, and ß are defined in the assembly section above.DPipe ODOuter diameter of the pipeE0Pitch Diameter at the Pipe's endE0=D - (O.O5*D + 1.1 ) * PL2Length of Last usefull ThreadLength of Last proper Thread. At L2, the thread profile starts to get truncated, but it is still considered "useful" until this point.E2Pitch Diameter at E2 planeE2 = E0 + 0.0625 *  L2VLength of Vanish threadsThe length of "Unuseful" threads.Basic Dimensions Chart – NPTF External ThreadsDimensions are in Inches. To view metric values, click the Thread Description link.There are a total of 20 parameters for each thread size. The below charts show only the main ones. To view all the parameters, click the thread description link.ThreadPipepipe ODTPIPitchEnd Pitch Diameter (E0)Engagement Length (L1)1/16 - 27 NPTF1/160.3125270.03700.271180.160001/8 - 27 NPTF1/80.4050270.03700.363510.161501/4 - 18 NPTF1/40.5400180.05560.477390.227803/8 - 18 NPTF3/80.6750180.05560.612010.240001/2 - 14 NPTF1/20.8400140.07140.758430.320003/4 - 14 NPTF3/41.0500140.07140.967680.339001 - 11 1/2 NPTF11.3150120.08701.213630.400001 1/4 - 11 1/2 NPTF1 1/41.6600120.08701.557130.420001 1/2 - 11 1/2 NPTF1 1/21.9000120.08701.796090.420002 - 11 1/2 NPTF22.3750120.08702.269020.436002 1/2 - 8 NPTF2 1/22.875080.12502.719530.682003 - 8 NPTF33.500080.12503.340620.76600NPTF Internal Thread DimensionsBasic DrawingProfile DrawingSymbols for NPTF Internal (Fitting Thread)SymbolNameExplnationP, H, h, L1, E1 α, and ß are defined in the assembly section above.E1Large End Pitch DiameterE1 = E0 + 0.0625 *  L1E3Small End Pitch DiameterE3 = E1 - 0.0625 *  (L1+L3)L3Length of Wrenching AllowanceTo create a seal, the pipe and fitting should be tightened by a wrench beyond the L1 plane by a minimum distance of L3.L1 + L3Thread LengthMinimum Internal Thread lengthTTap Drill SizeRecomended Drill diameter for tapping.Basic Dimensions Chart – NPTF Internal ThreadsDimensions are in Inches. To view metric values, click the Thread Description Link.There are a total of 15 parameters for each thread size. The below charts show only the main ones. To view all the parameters, click the thread description link. ThreadTPIPitchEnd Pitch Diameter (E1)Min Thread LengthTap Drill Size1/16 - 27 NPTF270.03700.281180.271100.240501/8 - 27 NPTF270.03700.373600.272600.332301/4 - 18 NPTF180.05560.491630.394500.431503/8 - 18 NPTF180.05560.627010.406700.565901/2 - 14 NPTF140.07140.778430.534300.698303/4 - 14 NPTF140.07140.988870.553300.906701 - 11 1/2 NPTF120.08701.238630.660901.139001 1/4 - 11 1/2 NPTF120.08701.583380.680901.480501 1/2 - 11 1/2 NPTF120.08701.822340.680901.717502 - 11 1/2 NPTF120.08702.296270.696902.186402 1/2 - 8 NPTF80.12502.762161.057002.605403 - 8 NPTF80.12503.388501.141003.22450Limits & Tolerances for NPTF threadsThe tolerancing system for NPTF resembles the NPT standard’s requirements but is more strict in several respects:Taper angle tolerance.Truncation tolerances.Required gauging.Taper Angle (ß) ToleranceThe taper angle (Beta) is defined in ASME B1-20.3 as 0.0625 +/-0.0050 Inch per an inch length. If we measure the pitch diameter at a particular location, move one inch along the axis and measure it again, we should measure a difference in diameter of 0.0625″.I have no idea why an angle is defined in such a peculiar way; however, you can convert it to degrees using the below formula:\( \beta = 0.5 \times \tan^{-1} \left( { 0.0625 } \right) = 1.79^{\circ}\)The linear units are measured on the diameter, and the angle is measured “per side”. Therefore the 0.5 factor is applied.The tolerance field is about 60% compared to the field in regular NPT threads.Truncation and Height TolerancesDimensions are in Inches.The ASTM standard provides only the tolerance of the truncations.We calculated the height limits based on that.The tolerances depend only on the pitch.The tolerance field is about 60% compared to the field in regular NPT threads.TPIThread HeightCrest TruncationRoot TruncationHead Anglehminhmaxfminfmaxfminfmax2α (60°)270.023380.026880.00170.00350.00350.0052+/- 2.5°180.037710.041210.00260.00430.00430.0061+/- 2°140.05140.05490.00260.00430.00430.0061+/- 2°11.50.062310.066610.00350.00520.00520.0078+/- 1.5°80.091850.096150.00520.00690.00690.0095+/- 1.5°Gauging for acceptanceThe NPT standard requires only an L1 Gage.NPTF requires, in addition to the L1 gage, also: L2, L3, and “Crest Check” gages.NPSF – Nation Pipe Straight Fuel ThreadNPSF threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered NPTF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSF threads are used with ductile materials that can adjust at assembly to the external taper during assembly.They should not be used in hard/brittle materials.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSF Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2768 - 0.28030.24820.311/8" - 27 NPSF0.3692 - 0.37270.34060.311/4" - 18 NPSF0.4852 - 0.49040.44220.473/8" - 18 NPSF0.6205 - 0.62570.57760.51/2" - 14 NPSF0.77 - 0.77670.71330.663/4" - 14 NPSF0.9805 - 0.98720.92380.661" - 11 1/2 NPSF1.2284 - 1.23651.160.78Dimensions in InchesNPSI – Nation Pipe Straight Intermediate ThreadNPSI threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered PTF-SAE short threads.They have slightly larger diameters than the NPSF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSI threads are used with hard/brittle materials that can adjust at assembly to the external taper during assembly.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSI Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2791 - 0.28260.25050.311/8" - 27 NPSF0.3715 - 0.3750.34290.311/4" - 18 NPSF0.4886 - 0.49380.44570.473/8" - 18 NPSF0.624 - 0.62920.58110.51/2" - 14 NPSF0.7745 - 0.78120.7180.663/4" - 14 NPSF0.985 - 0.99170.92830.661" - 11 1/2 NPSF1.2338 - 1.2421.16550.78Dimensions in InchesPTF-SAE Short ThreadExternalPTF-SAE Short External threads conform in all parameters with NPTF external threads, except that the thread length is shorter by one thread from the small (entering) end. They are designed for applications with limited clearance.They are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT external threads are intended for assembly with NPSI or NPTF internal threads.InternalPTF-SAE Short Internal threads conform in all parameters with NPTF internal threads, except that the thread length is shorter by one thread from the large (entering) end. They are designed for thin materials where thickness is insufficient for the full thread length of NPTFThey are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT internal threads are intended for assembly with NPTF external threads.They cannot be assembled with PTF-SAE short external threads.Related Glossary Terms:PitchL1 GagePress FitLength of EngagementDuctilityMajor DiameterTooth per inch (tpi)Pitch DiameterThread Height (Depth)Thread TruncationTap Drill SizeMinor Diameter

When is it necessary to use a mechanical seal?Using sealants could contaminate the fluids or gasses flowing through the system.A sealant might fail because of high heat or high pressure.List of Series defined in ASME B1-20.3NameDescriptionNPTFNational Pipe Taper FuelThe primary series for all service conditions.PTF-SAE ShortShort Pipe Tapar FuelSaves raw material where a full thread engagement length is not criticalNPSFNational Pipe Straight FuelInternal only straight thread for ductile materialsNPSINational Pipe Straight IntermediateInternal only straight thread for hard materialsDesignations of Dryseal Pipe ThreadsBasic designation syntax:Nominal Diameter in Inch FractionPitch in TPISeries: NPTF / PTF-SAE / NPSF / NPSI.DirectionDiameter:The diameters are given in inch fractions. For example, 1/4″, 3/4″, and 1 1/4″.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″).It is also allowed to denote the pitch by distance. For example, 1/4-0.05P means a thread with a pitch of 0.05″ (same as 20 TPI).Series:NPTF, PTF, NPSF, or NPSI. Where the meaning of each letter is:N = NationalP = PipeT = TaperS = StraightF = FuelI = IntermediateAdditional Parameters:Direction: By default, the thread is right-hand. For a left-hand thread, add the suffix -LH.NPTF series – National Pipe Taper Fuel ThreadNPTF stands for National Pipe Tapered Fuel. . The basic profile is identical to the common NPT thread. The main difference is that NPTF provides a leakproof seal without using a sealant. It is obtained by tight tolerances and gauging requirements that create interference fitting in all conditions. The thread profile is tapered at an angle of 1°47′ (0.0625 Inch per inch of length) relative to the axis. Learn more about the difference between NPTF & NPT.The profile properties, such as height, pitch, and truncations, are constant. However, the pitch diameter is not a constant value. It changes depending on the distance from the beginning of the thread. Because of that, the set of parameters and measuring techniques is very different (and often confusing) compared to Unified Inch and metric threads. To make the explanations and drawings more straightforward, we split them into 3 sections:An assembly drawing of an External and Internal thread showing only the parameters that are either common to both or are relevant to the assembly.External thread drawing with all its relevant dimensions.Internal thread drawing with all its relevant dimensions.Common Dimensions (External & Internal)When assembling with “hand force”, the male and female parts of a tapered thread will turn several rotations until the clearance is closed, and a “stop” is reached. This distance is called “Hand Tight Engagement Length”, and an “L1 Gauge usually measures it”. To form the seal, the assembly continues with a wrench an additional distance called “Wrench Allowance”.NPTF Pipe & Fitting Assembly DrawingSymbolsSymbolNameExplnationPpitchGiven in TPI, and used in calculations as distanceßThread Tapper AngleEquals 1°47' (1.7833°)Defined by ASME B1.20.3 as 0.0625 +/-0.0050 inch/inchαThread V half AngleEquals 30°Tolerance is defined in the below chartHHeight of the "sharp V"The height of the theoretical profile triangle.\( H=\frac{\sqrt{3}}{2}\times{P} \)hThread HeightDistance between the truncated root and crest. It is a result of the truncation tolerances as defined in the Below Chart.L1Length of hand-tight engagementThe maximum distance that the male and female parts can be threaded by normal hand force.E1Pitch diameter at the L1 PlaneThe Pitch d diameter at the plane of hand-tight engagement length (L1) of external thread (Pipe), and at the large end of internal thread (Fitting)L1 - L2Maximum Wrenching DistanceTo create a seal, the pipe and fitting should be further tightened by a wrench beyond the L1 plane.L3Minimum Wrenching DistanceNPTF External Thread DimensionsBasic DrawingProfile DrawingSymbolsSymbolNameExplnationP, H, h, L1, E1 α, and ß are defined in the assembly section above.DPipe ODOuter diameter of the pipeE0Pitch Diameter at the Pipe's endE0=D - (O.O5*D + 1.1 ) * PL2Length of Last usefull ThreadLength of Last proper Thread. At L2, the thread profile starts to get truncated, but it is still considered "useful" until this point.E2Pitch Diameter at E2 planeE2 = E0 + 0.0625 *  L2VLength of Vanish threadsThe length of "Unuseful" threads.Basic Dimensions Chart – NPTF External ThreadsDimensions are in Inches. To view metric values, click the Thread Description link.There are a total of 20 parameters for each thread size. The below charts show only the main ones. To view all the parameters, click the thread description link.ThreadPipepipe ODTPIPitchEnd Pitch Diameter (E0)Engagement Length (L1)1/16 - 27 NPTF1/160.3125270.03700.271180.160001/8 - 27 NPTF1/80.4050270.03700.363510.161501/4 - 18 NPTF1/40.5400180.05560.477390.227803/8 - 18 NPTF3/80.6750180.05560.612010.240001/2 - 14 NPTF1/20.8400140.07140.758430.320003/4 - 14 NPTF3/41.0500140.07140.967680.339001 - 11 1/2 NPTF11.3150120.08701.213630.400001 1/4 - 11 1/2 NPTF1 1/41.6600120.08701.557130.420001 1/2 - 11 1/2 NPTF1 1/21.9000120.08701.796090.420002 - 11 1/2 NPTF22.3750120.08702.269020.436002 1/2 - 8 NPTF2 1/22.875080.12502.719530.682003 - 8 NPTF33.500080.12503.340620.76600NPTF Internal Thread DimensionsBasic DrawingProfile DrawingSymbols for NPTF Internal (Fitting Thread)SymbolNameExplnationP, H, h, L1, E1 α, and ß are defined in the assembly section above.E1Large End Pitch DiameterE1 = E0 + 0.0625 *  L1E3Small End Pitch DiameterE3 = E1 - 0.0625 *  (L1+L3)L3Length of Wrenching AllowanceTo create a seal, the pipe and fitting should be tightened by a wrench beyond the L1 plane by a minimum distance of L3.L1 + L3Thread LengthMinimum Internal Thread lengthTTap Drill SizeRecomended Drill diameter for tapping.Basic Dimensions Chart – NPTF Internal ThreadsDimensions are in Inches. To view metric values, click the Thread Description Link.There are a total of 15 parameters for each thread size. The below charts show only the main ones. To view all the parameters, click the thread description link. ThreadTPIPitchEnd Pitch Diameter (E1)Min Thread LengthTap Drill Size1/16 - 27 NPTF270.03700.281180.271100.240501/8 - 27 NPTF270.03700.373600.272600.332301/4 - 18 NPTF180.05560.491630.394500.431503/8 - 18 NPTF180.05560.627010.406700.565901/2 - 14 NPTF140.07140.778430.534300.698303/4 - 14 NPTF140.07140.988870.553300.906701 - 11 1/2 NPTF120.08701.238630.660901.139001 1/4 - 11 1/2 NPTF120.08701.583380.680901.480501 1/2 - 11 1/2 NPTF120.08701.822340.680901.717502 - 11 1/2 NPTF120.08702.296270.696902.186402 1/2 - 8 NPTF80.12502.762161.057002.605403 - 8 NPTF80.12503.388501.141003.22450Limits & Tolerances for NPTF threadsThe tolerancing system for NPTF resembles the NPT standard’s requirements but is more strict in several respects:Taper angle tolerance.Truncation tolerances.Required gauging.Taper Angle (ß) ToleranceThe taper angle (Beta) is defined in ASME B1-20.3 as 0.0625 +/-0.0050 Inch per an inch length. If we measure the pitch diameter at a particular location, move one inch along the axis and measure it again, we should measure a difference in diameter of 0.0625″.I have no idea why an angle is defined in such a peculiar way; however, you can convert it to degrees using the below formula:\( \beta = 0.5 \times \tan^{-1} \left( { 0.0625 } \right) = 1.79^{\circ}\)The linear units are measured on the diameter, and the angle is measured “per side”. Therefore the 0.5 factor is applied.The tolerance field is about 60% compared to the field in regular NPT threads.Truncation and Height TolerancesDimensions are in Inches.The ASTM standard provides only the tolerance of the truncations.We calculated the height limits based on that.The tolerances depend only on the pitch.The tolerance field is about 60% compared to the field in regular NPT threads.TPIThread HeightCrest TruncationRoot TruncationHead Anglehminhmaxfminfmaxfminfmax2α (60°)270.023380.026880.00170.00350.00350.0052+/- 2.5°180.037710.041210.00260.00430.00430.0061+/- 2°140.05140.05490.00260.00430.00430.0061+/- 2°11.50.062310.066610.00350.00520.00520.0078+/- 1.5°80.091850.096150.00520.00690.00690.0095+/- 1.5°Gauging for acceptanceThe NPT standard requires only an L1 Gage.NPTF requires, in addition to the L1 gage, also: L2, L3, and “Crest Check” gages.NPSF – Nation Pipe Straight Fuel ThreadNPSF threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered NPTF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSF threads are used with ductile materials that can adjust at assembly to the external taper during assembly.They should not be used in hard/brittle materials.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSF Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2768 - 0.28030.24820.311/8" - 27 NPSF0.3692 - 0.37270.34060.311/4" - 18 NPSF0.4852 - 0.49040.44220.473/8" - 18 NPSF0.6205 - 0.62570.57760.51/2" - 14 NPSF0.77 - 0.77670.71330.663/4" - 14 NPSF0.9805 - 0.98720.92380.661" - 11 1/2 NPSF1.2284 - 1.23651.160.78Dimensions in InchesNPSI – Nation Pipe Straight Intermediate ThreadNPSI threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered PTF-SAE short threads.They have slightly larger diameters than the NPSF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSI threads are used with hard/brittle materials that can adjust at assembly to the external taper during assembly.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSI Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2791 - 0.28260.25050.311/8" - 27 NPSF0.3715 - 0.3750.34290.311/4" - 18 NPSF0.4886 - 0.49380.44570.473/8" - 18 NPSF0.624 - 0.62920.58110.51/2" - 14 NPSF0.7745 - 0.78120.7180.663/4" - 14 NPSF0.985 - 0.99170.92830.661" - 11 1/2 NPSF1.2338 - 1.2421.16550.78Dimensions in InchesPTF-SAE Short ThreadExternalPTF-SAE Short External threads conform in all parameters with NPTF external threads, except that the thread length is shorter by one thread from the small (entering) end. They are designed for applications with limited clearance.They are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT external threads are intended for assembly with NPSI or NPTF internal threads.InternalPTF-SAE Short Internal threads conform in all parameters with NPTF internal threads, except that the thread length is shorter by one thread from the large (entering) end. They are designed for thin materials where thickness is insufficient for the full thread length of NPTFThey are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT internal threads are intended for assembly with NPTF external threads.They cannot be assembled with PTF-SAE short external threads.Related Glossary Terms:PitchL1 GagePress FitLength of EngagementDuctilityMajor DiameterTooth per inch (tpi)Pitch DiameterThread Height (Depth)Thread TruncationTap Drill SizeMinor Diameter

Carbide drill bits are the pinnacle of strength and durability. These bits have carbon and heavy metals, such as tungsten, in their composition. With heavy metal compounds, carbide becomes the hardest of all metals, making them suitable for drilling into hardened steel and high-density materials. You won’t go wrong when using carbide because they don’t rust and are especially impactful in easily boring through concrete, brick, and stone.

NPT vsNPTFthread dimensions

NPTFvs NPT

The tolerancing system for NPTF resembles the NPT standard’s requirements but is more strict in several respects:Taper angle tolerance.Truncation tolerances.Required gauging.

Drill bits are an asset in your toolbox because they help drilling projects turn out the right (and only) time. Whether you’re a seasoned woodworker or a metal fabrication enthusiast, your choice of drill bit materials can spell the difference between a project executed with precision and one that’s subpar. If you’re curious to know if the drill bit you have will help or hinder you, learn about it in this ultimate guide to different drill bit materials.

NPTFfittings

Before you return the bit set, consider learning what a typical twist bit has, such as a shank that fits into the drills chuck. Then, there’s the flute—the spiral groove that removes the chips from the hole. Now you have the body—this is the main part of the drill bit that lacks flutes or margins. Like its relative, the nail, your bits point has a sharp end. The cutting lips are the edges that do the actual cutting.

The profile properties, such as height, pitch, and truncations, are constant. However, the pitch diameter is not a constant value. It changes depending on the distance from the beginning of the thread. Because of that, the set of parameters and measuring techniques is very different (and often confusing) compared to Unified Inch and metric threads. To make the explanations and drawings more straightforward, we split them into 3 sections:An assembly drawing of an External and Internal thread showing only the parameters that are either common to both or are relevant to the assembly.External thread drawing with all its relevant dimensions.Internal thread drawing with all its relevant dimensions.Common Dimensions (External & Internal)When assembling with “hand force”, the male and female parts of a tapered thread will turn several rotations until the clearance is closed, and a “stop” is reached. This distance is called “Hand Tight Engagement Length”, and an “L1 Gauge usually measures it”. To form the seal, the assembly continues with a wrench an additional distance called “Wrench Allowance”.NPTF Pipe & Fitting Assembly DrawingSymbolsSymbolNameExplnationPpitchGiven in TPI, and used in calculations as distanceßThread Tapper AngleEquals 1°47' (1.7833°)Defined by ASME B1.20.3 as 0.0625 +/-0.0050 inch/inchαThread V half AngleEquals 30°Tolerance is defined in the below chartHHeight of the "sharp V"The height of the theoretical profile triangle.\( H=\frac{\sqrt{3}}{2}\times{P} \)hThread HeightDistance between the truncated root and crest. It is a result of the truncation tolerances as defined in the Below Chart.L1Length of hand-tight engagementThe maximum distance that the male and female parts can be threaded by normal hand force.E1Pitch diameter at the L1 PlaneThe Pitch d diameter at the plane of hand-tight engagement length (L1) of external thread (Pipe), and at the large end of internal thread (Fitting)L1 - L2Maximum Wrenching DistanceTo create a seal, the pipe and fitting should be further tightened by a wrench beyond the L1 plane.L3Minimum Wrenching DistanceNPTF External Thread DimensionsBasic DrawingProfile DrawingSymbolsSymbolNameExplnationP, H, h, L1, E1 α, and ß are defined in the assembly section above.DPipe ODOuter diameter of the pipeE0Pitch Diameter at the Pipe's endE0=D - (O.O5*D + 1.1 ) * PL2Length of Last usefull ThreadLength of Last proper Thread. At L2, the thread profile starts to get truncated, but it is still considered "useful" until this point.E2Pitch Diameter at E2 planeE2 = E0 + 0.0625 *  L2VLength of Vanish threadsThe length of "Unuseful" threads.Basic Dimensions Chart – NPTF External ThreadsDimensions are in Inches. To view metric values, click the Thread Description link.There are a total of 20 parameters for each thread size. The below charts show only the main ones. To view all the parameters, click the thread description link.ThreadPipepipe ODTPIPitchEnd Pitch Diameter (E0)Engagement Length (L1)1/16 - 27 NPTF1/160.3125270.03700.271180.160001/8 - 27 NPTF1/80.4050270.03700.363510.161501/4 - 18 NPTF1/40.5400180.05560.477390.227803/8 - 18 NPTF3/80.6750180.05560.612010.240001/2 - 14 NPTF1/20.8400140.07140.758430.320003/4 - 14 NPTF3/41.0500140.07140.967680.339001 - 11 1/2 NPTF11.3150120.08701.213630.400001 1/4 - 11 1/2 NPTF1 1/41.6600120.08701.557130.420001 1/2 - 11 1/2 NPTF1 1/21.9000120.08701.796090.420002 - 11 1/2 NPTF22.3750120.08702.269020.436002 1/2 - 8 NPTF2 1/22.875080.12502.719530.682003 - 8 NPTF33.500080.12503.340620.76600NPTF Internal Thread DimensionsBasic DrawingProfile DrawingSymbols for NPTF Internal (Fitting Thread)SymbolNameExplnationP, H, h, L1, E1 α, and ß are defined in the assembly section above.E1Large End Pitch DiameterE1 = E0 + 0.0625 *  L1E3Small End Pitch DiameterE3 = E1 - 0.0625 *  (L1+L3)L3Length of Wrenching AllowanceTo create a seal, the pipe and fitting should be tightened by a wrench beyond the L1 plane by a minimum distance of L3.L1 + L3Thread LengthMinimum Internal Thread lengthTTap Drill SizeRecomended Drill diameter for tapping.Basic Dimensions Chart – NPTF Internal ThreadsDimensions are in Inches. To view metric values, click the Thread Description Link.There are a total of 15 parameters for each thread size. The below charts show only the main ones. To view all the parameters, click the thread description link. ThreadTPIPitchEnd Pitch Diameter (E1)Min Thread LengthTap Drill Size1/16 - 27 NPTF270.03700.281180.271100.240501/8 - 27 NPTF270.03700.373600.272600.332301/4 - 18 NPTF180.05560.491630.394500.431503/8 - 18 NPTF180.05560.627010.406700.565901/2 - 14 NPTF140.07140.778430.534300.698303/4 - 14 NPTF140.07140.988870.553300.906701 - 11 1/2 NPTF120.08701.238630.660901.139001 1/4 - 11 1/2 NPTF120.08701.583380.680901.480501 1/2 - 11 1/2 NPTF120.08701.822340.680901.717502 - 11 1/2 NPTF120.08702.296270.696902.186402 1/2 - 8 NPTF80.12502.762161.057002.605403 - 8 NPTF80.12503.388501.141003.22450Limits & Tolerances for NPTF threadsThe tolerancing system for NPTF resembles the NPT standard’s requirements but is more strict in several respects:Taper angle tolerance.Truncation tolerances.Required gauging.Taper Angle (ß) ToleranceThe taper angle (Beta) is defined in ASME B1-20.3 as 0.0625 +/-0.0050 Inch per an inch length. If we measure the pitch diameter at a particular location, move one inch along the axis and measure it again, we should measure a difference in diameter of 0.0625″.I have no idea why an angle is defined in such a peculiar way; however, you can convert it to degrees using the below formula:\( \beta = 0.5 \times \tan^{-1} \left( { 0.0625 } \right) = 1.79^{\circ}\)The linear units are measured on the diameter, and the angle is measured “per side”. Therefore the 0.5 factor is applied.The tolerance field is about 60% compared to the field in regular NPT threads.Truncation and Height TolerancesDimensions are in Inches.The ASTM standard provides only the tolerance of the truncations.We calculated the height limits based on that.The tolerances depend only on the pitch.The tolerance field is about 60% compared to the field in regular NPT threads.TPIThread HeightCrest TruncationRoot TruncationHead Anglehminhmaxfminfmaxfminfmax2α (60°)270.023380.026880.00170.00350.00350.0052+/- 2.5°180.037710.041210.00260.00430.00430.0061+/- 2°140.05140.05490.00260.00430.00430.0061+/- 2°11.50.062310.066610.00350.00520.00520.0078+/- 1.5°80.091850.096150.00520.00690.00690.0095+/- 1.5°Gauging for acceptanceThe NPT standard requires only an L1 Gage.NPTF requires, in addition to the L1 gage, also: L2, L3, and “Crest Check” gages.NPSF – Nation Pipe Straight Fuel ThreadNPSF threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered NPTF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSF threads are used with ductile materials that can adjust at assembly to the external taper during assembly.They should not be used in hard/brittle materials.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSF Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2768 - 0.28030.24820.311/8" - 27 NPSF0.3692 - 0.37270.34060.311/4" - 18 NPSF0.4852 - 0.49040.44220.473/8" - 18 NPSF0.6205 - 0.62570.57760.51/2" - 14 NPSF0.77 - 0.77670.71330.663/4" - 14 NPSF0.9805 - 0.98720.92380.661" - 11 1/2 NPSF1.2284 - 1.23651.160.78Dimensions in InchesNPSI – Nation Pipe Straight Intermediate ThreadNPSI threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered PTF-SAE short threads.They have slightly larger diameters than the NPSF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSI threads are used with hard/brittle materials that can adjust at assembly to the external taper during assembly.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSI Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2791 - 0.28260.25050.311/8" - 27 NPSF0.3715 - 0.3750.34290.311/4" - 18 NPSF0.4886 - 0.49380.44570.473/8" - 18 NPSF0.624 - 0.62920.58110.51/2" - 14 NPSF0.7745 - 0.78120.7180.663/4" - 14 NPSF0.985 - 0.99170.92830.661" - 11 1/2 NPSF1.2338 - 1.2421.16550.78Dimensions in InchesPTF-SAE Short ThreadExternalPTF-SAE Short External threads conform in all parameters with NPTF external threads, except that the thread length is shorter by one thread from the small (entering) end. They are designed for applications with limited clearance.They are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT external threads are intended for assembly with NPSI or NPTF internal threads.InternalPTF-SAE Short Internal threads conform in all parameters with NPTF internal threads, except that the thread length is shorter by one thread from the large (entering) end. They are designed for thin materials where thickness is insufficient for the full thread length of NPTFThey are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT internal threads are intended for assembly with NPTF external threads.They cannot be assembled with PTF-SAE short external threads.Related Glossary Terms:PitchL1 GagePress FitLength of EngagementDuctilityMajor DiameterTooth per inch (tpi)Pitch DiameterThread Height (Depth)Thread TruncationTap Drill SizeMinor Diameter

When assembling with “hand force”, the male and female parts of a tapered thread will turn several rotations until the clearance is closed, and a “stop” is reached. This distance is called “Hand Tight Engagement Length”, and an “L1 Gauge usually measures it”. To form the seal, the assembly continues with a wrench an additional distance called “Wrench Allowance”.NPTF Pipe & Fitting Assembly DrawingSymbolsSymbolNameExplnationPpitchGiven in TPI, and used in calculations as distanceßThread Tapper AngleEquals 1°47' (1.7833°)Defined by ASME B1.20.3 as 0.0625 +/-0.0050 inch/inchαThread V half AngleEquals 30°Tolerance is defined in the below chartHHeight of the "sharp V"The height of the theoretical profile triangle.\( H=\frac{\sqrt{3}}{2}\times{P} \)hThread HeightDistance between the truncated root and crest. It is a result of the truncation tolerances as defined in the Below Chart.L1Length of hand-tight engagementThe maximum distance that the male and female parts can be threaded by normal hand force.E1Pitch diameter at the L1 PlaneThe Pitch d diameter at the plane of hand-tight engagement length (L1) of external thread (Pipe), and at the large end of internal thread (Fitting)L1 - L2Maximum Wrenching DistanceTo create a seal, the pipe and fitting should be further tightened by a wrench beyond the L1 plane.L3Minimum Wrenching DistanceNPTF External Thread DimensionsBasic DrawingProfile DrawingSymbolsSymbolNameExplnationP, H, h, L1, E1 α, and ß are defined in the assembly section above.DPipe ODOuter diameter of the pipeE0Pitch Diameter at the Pipe's endE0=D - (O.O5*D + 1.1 ) * PL2Length of Last usefull ThreadLength of Last proper Thread. At L2, the thread profile starts to get truncated, but it is still considered "useful" until this point.E2Pitch Diameter at E2 planeE2 = E0 + 0.0625 *  L2VLength of Vanish threadsThe length of "Unuseful" threads.Basic Dimensions Chart – NPTF External ThreadsDimensions are in Inches. To view metric values, click the Thread Description link.There are a total of 20 parameters for each thread size. The below charts show only the main ones. To view all the parameters, click the thread description link.ThreadPipepipe ODTPIPitchEnd Pitch Diameter (E0)Engagement Length (L1)1/16 - 27 NPTF1/160.3125270.03700.271180.160001/8 - 27 NPTF1/80.4050270.03700.363510.161501/4 - 18 NPTF1/40.5400180.05560.477390.227803/8 - 18 NPTF3/80.6750180.05560.612010.240001/2 - 14 NPTF1/20.8400140.07140.758430.320003/4 - 14 NPTF3/41.0500140.07140.967680.339001 - 11 1/2 NPTF11.3150120.08701.213630.400001 1/4 - 11 1/2 NPTF1 1/41.6600120.08701.557130.420001 1/2 - 11 1/2 NPTF1 1/21.9000120.08701.796090.420002 - 11 1/2 NPTF22.3750120.08702.269020.436002 1/2 - 8 NPTF2 1/22.875080.12502.719530.682003 - 8 NPTF33.500080.12503.340620.76600NPTF Internal Thread DimensionsBasic DrawingProfile DrawingSymbols for NPTF Internal (Fitting Thread)SymbolNameExplnationP, H, h, L1, E1 α, and ß are defined in the assembly section above.E1Large End Pitch DiameterE1 = E0 + 0.0625 *  L1E3Small End Pitch DiameterE3 = E1 - 0.0625 *  (L1+L3)L3Length of Wrenching AllowanceTo create a seal, the pipe and fitting should be tightened by a wrench beyond the L1 plane by a minimum distance of L3.L1 + L3Thread LengthMinimum Internal Thread lengthTTap Drill SizeRecomended Drill diameter for tapping.Basic Dimensions Chart – NPTF Internal ThreadsDimensions are in Inches. To view metric values, click the Thread Description Link.There are a total of 15 parameters for each thread size. The below charts show only the main ones. To view all the parameters, click the thread description link. ThreadTPIPitchEnd Pitch Diameter (E1)Min Thread LengthTap Drill Size1/16 - 27 NPTF270.03700.281180.271100.240501/8 - 27 NPTF270.03700.373600.272600.332301/4 - 18 NPTF180.05560.491630.394500.431503/8 - 18 NPTF180.05560.627010.406700.565901/2 - 14 NPTF140.07140.778430.534300.698303/4 - 14 NPTF140.07140.988870.553300.906701 - 11 1/2 NPTF120.08701.238630.660901.139001 1/4 - 11 1/2 NPTF120.08701.583380.680901.480501 1/2 - 11 1/2 NPTF120.08701.822340.680901.717502 - 11 1/2 NPTF120.08702.296270.696902.186402 1/2 - 8 NPTF80.12502.762161.057002.605403 - 8 NPTF80.12503.388501.141003.22450Limits & Tolerances for NPTF threadsThe tolerancing system for NPTF resembles the NPT standard’s requirements but is more strict in several respects:Taper angle tolerance.Truncation tolerances.Required gauging.Taper Angle (ß) ToleranceThe taper angle (Beta) is defined in ASME B1-20.3 as 0.0625 +/-0.0050 Inch per an inch length. If we measure the pitch diameter at a particular location, move one inch along the axis and measure it again, we should measure a difference in diameter of 0.0625″.I have no idea why an angle is defined in such a peculiar way; however, you can convert it to degrees using the below formula:\( \beta = 0.5 \times \tan^{-1} \left( { 0.0625 } \right) = 1.79^{\circ}\)The linear units are measured on the diameter, and the angle is measured “per side”. Therefore the 0.5 factor is applied.The tolerance field is about 60% compared to the field in regular NPT threads.Truncation and Height TolerancesDimensions are in Inches.The ASTM standard provides only the tolerance of the truncations.We calculated the height limits based on that.The tolerances depend only on the pitch.The tolerance field is about 60% compared to the field in regular NPT threads.TPIThread HeightCrest TruncationRoot TruncationHead Anglehminhmaxfminfmaxfminfmax2α (60°)270.023380.026880.00170.00350.00350.0052+/- 2.5°180.037710.041210.00260.00430.00430.0061+/- 2°140.05140.05490.00260.00430.00430.0061+/- 2°11.50.062310.066610.00350.00520.00520.0078+/- 1.5°80.091850.096150.00520.00690.00690.0095+/- 1.5°Gauging for acceptanceThe NPT standard requires only an L1 Gage.NPTF requires, in addition to the L1 gage, also: L2, L3, and “Crest Check” gages.NPSF – Nation Pipe Straight Fuel ThreadNPSF threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered NPTF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSF threads are used with ductile materials that can adjust at assembly to the external taper during assembly.They should not be used in hard/brittle materials.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSF Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2768 - 0.28030.24820.311/8" - 27 NPSF0.3692 - 0.37270.34060.311/4" - 18 NPSF0.4852 - 0.49040.44220.473/8" - 18 NPSF0.6205 - 0.62570.57760.51/2" - 14 NPSF0.77 - 0.77670.71330.663/4" - 14 NPSF0.9805 - 0.98720.92380.661" - 11 1/2 NPSF1.2284 - 1.23651.160.78Dimensions in InchesNPSI – Nation Pipe Straight Intermediate ThreadNPSI threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered PTF-SAE short threads.They have slightly larger diameters than the NPSF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSI threads are used with hard/brittle materials that can adjust at assembly to the external taper during assembly.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSI Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2791 - 0.28260.25050.311/8" - 27 NPSF0.3715 - 0.3750.34290.311/4" - 18 NPSF0.4886 - 0.49380.44570.473/8" - 18 NPSF0.624 - 0.62920.58110.51/2" - 14 NPSF0.7745 - 0.78120.7180.663/4" - 14 NPSF0.985 - 0.99170.92830.661" - 11 1/2 NPSF1.2338 - 1.2421.16550.78Dimensions in InchesPTF-SAE Short ThreadExternalPTF-SAE Short External threads conform in all parameters with NPTF external threads, except that the thread length is shorter by one thread from the small (entering) end. They are designed for applications with limited clearance.They are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT external threads are intended for assembly with NPSI or NPTF internal threads.InternalPTF-SAE Short Internal threads conform in all parameters with NPTF internal threads, except that the thread length is shorter by one thread from the large (entering) end. They are designed for thin materials where thickness is insufficient for the full thread length of NPTFThey are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT internal threads are intended for assembly with NPTF external threads.They cannot be assembled with PTF-SAE short external threads.Related Glossary Terms:PitchL1 GagePress FitLength of EngagementDuctilityMajor DiameterTooth per inch (tpi)Pitch DiameterThread Height (Depth)Thread TruncationTap Drill SizeMinor Diameter

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Additional Parameters:Direction: By default, the thread is right-hand. For a left-hand thread, add the suffix -LH.NPTF series – National Pipe Taper Fuel ThreadNPTF stands for National Pipe Tapered Fuel. . The basic profile is identical to the common NPT thread. The main difference is that NPTF provides a leakproof seal without using a sealant. It is obtained by tight tolerances and gauging requirements that create interference fitting in all conditions. The thread profile is tapered at an angle of 1°47′ (0.0625 Inch per inch of length) relative to the axis. Learn more about the difference between NPTF & NPT.The profile properties, such as height, pitch, and truncations, are constant. However, the pitch diameter is not a constant value. It changes depending on the distance from the beginning of the thread. Because of that, the set of parameters and measuring techniques is very different (and often confusing) compared to Unified Inch and metric threads. To make the explanations and drawings more straightforward, we split them into 3 sections:An assembly drawing of an External and Internal thread showing only the parameters that are either common to both or are relevant to the assembly.External thread drawing with all its relevant dimensions.Internal thread drawing with all its relevant dimensions.Common Dimensions (External & Internal)When assembling with “hand force”, the male and female parts of a tapered thread will turn several rotations until the clearance is closed, and a “stop” is reached. This distance is called “Hand Tight Engagement Length”, and an “L1 Gauge usually measures it”. To form the seal, the assembly continues with a wrench an additional distance called “Wrench Allowance”.NPTF Pipe & Fitting Assembly DrawingSymbolsSymbolNameExplnationPpitchGiven in TPI, and used in calculations as distanceßThread Tapper AngleEquals 1°47' (1.7833°)Defined by ASME B1.20.3 as 0.0625 +/-0.0050 inch/inchαThread V half AngleEquals 30°Tolerance is defined in the below chartHHeight of the "sharp V"The height of the theoretical profile triangle.\( H=\frac{\sqrt{3}}{2}\times{P} \)hThread HeightDistance between the truncated root and crest. It is a result of the truncation tolerances as defined in the Below Chart.L1Length of hand-tight engagementThe maximum distance that the male and female parts can be threaded by normal hand force.E1Pitch diameter at the L1 PlaneThe Pitch d diameter at the plane of hand-tight engagement length (L1) of external thread (Pipe), and at the large end of internal thread (Fitting)L1 - L2Maximum Wrenching DistanceTo create a seal, the pipe and fitting should be further tightened by a wrench beyond the L1 plane.L3Minimum Wrenching DistanceNPTF External Thread DimensionsBasic DrawingProfile DrawingSymbolsSymbolNameExplnationP, H, h, L1, E1 α, and ß are defined in the assembly section above.DPipe ODOuter diameter of the pipeE0Pitch Diameter at the Pipe's endE0=D - (O.O5*D + 1.1 ) * PL2Length of Last usefull ThreadLength of Last proper Thread. At L2, the thread profile starts to get truncated, but it is still considered "useful" until this point.E2Pitch Diameter at E2 planeE2 = E0 + 0.0625 *  L2VLength of Vanish threadsThe length of "Unuseful" threads.Basic Dimensions Chart – NPTF External ThreadsDimensions are in Inches. To view metric values, click the Thread Description link.There are a total of 20 parameters for each thread size. The below charts show only the main ones. To view all the parameters, click the thread description link.ThreadPipepipe ODTPIPitchEnd Pitch Diameter (E0)Engagement Length (L1)1/16 - 27 NPTF1/160.3125270.03700.271180.160001/8 - 27 NPTF1/80.4050270.03700.363510.161501/4 - 18 NPTF1/40.5400180.05560.477390.227803/8 - 18 NPTF3/80.6750180.05560.612010.240001/2 - 14 NPTF1/20.8400140.07140.758430.320003/4 - 14 NPTF3/41.0500140.07140.967680.339001 - 11 1/2 NPTF11.3150120.08701.213630.400001 1/4 - 11 1/2 NPTF1 1/41.6600120.08701.557130.420001 1/2 - 11 1/2 NPTF1 1/21.9000120.08701.796090.420002 - 11 1/2 NPTF22.3750120.08702.269020.436002 1/2 - 8 NPTF2 1/22.875080.12502.719530.682003 - 8 NPTF33.500080.12503.340620.76600NPTF Internal Thread DimensionsBasic DrawingProfile DrawingSymbols for NPTF Internal (Fitting Thread)SymbolNameExplnationP, H, h, L1, E1 α, and ß are defined in the assembly section above.E1Large End Pitch DiameterE1 = E0 + 0.0625 *  L1E3Small End Pitch DiameterE3 = E1 - 0.0625 *  (L1+L3)L3Length of Wrenching AllowanceTo create a seal, the pipe and fitting should be tightened by a wrench beyond the L1 plane by a minimum distance of L3.L1 + L3Thread LengthMinimum Internal Thread lengthTTap Drill SizeRecomended Drill diameter for tapping.Basic Dimensions Chart – NPTF Internal ThreadsDimensions are in Inches. To view metric values, click the Thread Description Link.There are a total of 15 parameters for each thread size. The below charts show only the main ones. To view all the parameters, click the thread description link. ThreadTPIPitchEnd Pitch Diameter (E1)Min Thread LengthTap Drill Size1/16 - 27 NPTF270.03700.281180.271100.240501/8 - 27 NPTF270.03700.373600.272600.332301/4 - 18 NPTF180.05560.491630.394500.431503/8 - 18 NPTF180.05560.627010.406700.565901/2 - 14 NPTF140.07140.778430.534300.698303/4 - 14 NPTF140.07140.988870.553300.906701 - 11 1/2 NPTF120.08701.238630.660901.139001 1/4 - 11 1/2 NPTF120.08701.583380.680901.480501 1/2 - 11 1/2 NPTF120.08701.822340.680901.717502 - 11 1/2 NPTF120.08702.296270.696902.186402 1/2 - 8 NPTF80.12502.762161.057002.605403 - 8 NPTF80.12503.388501.141003.22450Limits & Tolerances for NPTF threadsThe tolerancing system for NPTF resembles the NPT standard’s requirements but is more strict in several respects:Taper angle tolerance.Truncation tolerances.Required gauging.Taper Angle (ß) ToleranceThe taper angle (Beta) is defined in ASME B1-20.3 as 0.0625 +/-0.0050 Inch per an inch length. If we measure the pitch diameter at a particular location, move one inch along the axis and measure it again, we should measure a difference in diameter of 0.0625″.I have no idea why an angle is defined in such a peculiar way; however, you can convert it to degrees using the below formula:\( \beta = 0.5 \times \tan^{-1} \left( { 0.0625 } \right) = 1.79^{\circ}\)The linear units are measured on the diameter, and the angle is measured “per side”. Therefore the 0.5 factor is applied.The tolerance field is about 60% compared to the field in regular NPT threads.Truncation and Height TolerancesDimensions are in Inches.The ASTM standard provides only the tolerance of the truncations.We calculated the height limits based on that.The tolerances depend only on the pitch.The tolerance field is about 60% compared to the field in regular NPT threads.TPIThread HeightCrest TruncationRoot TruncationHead Anglehminhmaxfminfmaxfminfmax2α (60°)270.023380.026880.00170.00350.00350.0052+/- 2.5°180.037710.041210.00260.00430.00430.0061+/- 2°140.05140.05490.00260.00430.00430.0061+/- 2°11.50.062310.066610.00350.00520.00520.0078+/- 1.5°80.091850.096150.00520.00690.00690.0095+/- 1.5°Gauging for acceptanceThe NPT standard requires only an L1 Gage.NPTF requires, in addition to the L1 gage, also: L2, L3, and “Crest Check” gages.NPSF – Nation Pipe Straight Fuel ThreadNPSF threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered NPTF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSF threads are used with ductile materials that can adjust at assembly to the external taper during assembly.They should not be used in hard/brittle materials.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSF Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2768 - 0.28030.24820.311/8" - 27 NPSF0.3692 - 0.37270.34060.311/4" - 18 NPSF0.4852 - 0.49040.44220.473/8" - 18 NPSF0.6205 - 0.62570.57760.51/2" - 14 NPSF0.77 - 0.77670.71330.663/4" - 14 NPSF0.9805 - 0.98720.92380.661" - 11 1/2 NPSF1.2284 - 1.23651.160.78Dimensions in InchesNPSI – Nation Pipe Straight Intermediate ThreadNPSI threads are straight (cylindrical) instead of tapered.They are internal only, intended to mate with external tapered PTF-SAE short threads.They have slightly larger diameters than the NPSF threads. They are more economical to manufacture than tapered threads.Sealing is not guaranteed since root and crest interference will not occur for all threads. NPSI threads are used with hard/brittle materials that can adjust at assembly to the external taper during assembly.Since they are cylindrical, the definition of pitch, major and minor diameters are more in-line with the methods used in regular metric or inch threads.NPSI Thread Dimensions chartThreadPitch DiameterMin. Minor DiameterMin. Thread Length1/16" - 27 NPSF0.2791 - 0.28260.25050.311/8" - 27 NPSF0.3715 - 0.3750.34290.311/4" - 18 NPSF0.4886 - 0.49380.44570.473/8" - 18 NPSF0.624 - 0.62920.58110.51/2" - 14 NPSF0.7745 - 0.78120.7180.663/4" - 14 NPSF0.985 - 0.99170.92830.661" - 11 1/2 NPSF1.2338 - 1.2421.16550.78Dimensions in InchesPTF-SAE Short ThreadExternalPTF-SAE Short External threads conform in all parameters with NPTF external threads, except that the thread length is shorter by one thread from the small (entering) end. They are designed for applications with limited clearance.They are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT external threads are intended for assembly with NPSI or NPTF internal threads.InternalPTF-SAE Short Internal threads conform in all parameters with NPTF internal threads, except that the thread length is shorter by one thread from the large (entering) end. They are designed for thin materials where thickness is insufficient for the full thread length of NPTFThey are slightly cheaper to produce than standard NPTF threads.PTF-SAE SHORT internal threads are intended for assembly with NPTF external threads.They cannot be assembled with PTF-SAE short external threads.Related Glossary Terms:PitchL1 GagePress FitLength of EngagementDuctilityMajor DiameterTooth per inch (tpi)Pitch DiameterThread Height (Depth)Thread TruncationTap Drill SizeMinor Diameter

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