Blocked couplings not removable or demountable with hot press. For the coupled parts that must behave as a single piece, suitable to transmit axial loads and torques without the use of keys or similar systems.

Slipping fits of parts with great tolerances. The parts can easily be slid one into the other and turn.

Blocked couplings not removable or demountable with hot press. For the coupled parts that must be as a single piece, suitable to transmit axial loads and torques without the use of keys or similar systems.

For components that must be disassembled very free respect to one another with abundant mechanical play: operating temperature much higher than the one at mounting.

For couplings slightly blocked, difficulty removable by hand, preferably for long seats and to be secured against mutual rotation.

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(*) This coupling is classified by all the texts as transition fit, although there is never play in any combination of values between the shaft and the hole.

Blocked couplings not removable or demountable with hot press. For the coupled parts that must be as a single piece, suitable to transmit axial loads and torques without the use of keys or similar systems.

For components with very strong blocking, with disassembly practicable only by substitution of one of the components.

For components that have to be disassembled very free respect to each other with abundant mechanical play.

Rotating couplings with average peripheral speed (2-4 m/s), with need of limited plays.

Fits of long shafts, e.g. in agricultural machines, bearings of pumps, fans and piston machines.

Couplings sliding axially lubricated, with no need of precision, with long seat or with low loads.

Precision couplings, with seat generally short, of parts mutually fixed, extractable by hand. Ex .: Spare wheels mounted with keyways or splined shafts.

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Free running fit not for use where accuracy is essential, but good for large temperature variations, high running speeds, or heavy journal pressures.

For very fast rotating components, even with imperfect centering and sustenance not perfectly hydrodynamics and good mechanical play.

For components that can move if lubricated respect to one another, with slow motion.

Pressed fits with big interferences. Assembly using pressing and great forces under different temperatures of the parts.

Parts of machine tools, sliding gears and clutch disks, crankshaft journals, pistons of hydraulic machines, rods sliding in bearings, grinding machine spindles.

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For components which must not run too easily with respect to each other, but that can be easily assembled and disassembled, secured against rotation and sliding.

Components mutually fixed, assembled and disassembled by hand or with little effort; fixed centering seats with good precision. Parts to be secured against rotation and sliding.

For components of high precision which can move respect to one another with slow motion.

Note: For economic reasons, the first choice for a fit should, whenever possible, be made from the tolerance classes shown with green color.

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Sliding fits with very small clearances for precise guiding and centering of parts. Mounting by sliding on without use of any great force, after lubrication the parts can be turned and slid by hand.

Pressed fits with medium interference. Assembly of parts using hot pressing. Assembly using cold pressing only with use of large forces.

Ex .: High speed shafts, in general in its bushings. Positioning pins with medium accuracy.

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Pivots, latches, fits of parts exposed to corrosive effects, contamination with dust and thermal or mechanical deformations.

This section reports a summary of the available information that can be found on technical literature about the fit tolerance between shafts and holes.

Couplings secured against mutual rotation by keyways, pins, etc., easily removable. Ex .: keying of ball bearings and roller bearings. Keyways. Fixing joints in general.

For components fixed respect to one another, which can be mounted only by strong pressure; normally the two parts must be secured against rotation and sliding. Ex.: Couplings without keyways to transmit low torques.

For components that have to be disassembled very free respect to each other with abundant mechanical play.

Blocked couplings not removable or demountable with hot press. For the coupled parts that must behave as a single piece, suitable to transmit axial loads and torques without the use of keys or similar systems.

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Components fixed respect to each other, assembled and disassembled without excessive pressure and secured against rotation and sliding.

For components mutually fixed, assembled and demontable by hand or with little effort; fixed centering seats with good precision. Parts to be secured against rotation and sliding.

For components that must be disassembled very free respect to each other with abundant mechanical play: operating temperature much higher than the one at mounting.

For components with high precision sliding axially, or equipped with rotary slow or oscillatory motion, with internal lubrication.

Fixed components with respect to each other and secured against rotation and sliding.

For components which must not slide too easily respect to one another, but that can be easily assembled and disassembled, secured against rotation and sliding.

For components that must be disassembled very free respect to one another with abundant mechanical play: operating temperature much higher than the one at mounting.

Demountable fits of hubs of gears and pulleys, manual wheels, clutches, brake disks.

Running fits with very small clearances for accurate guiding of shafts. Without any noticeable clearance after assembly.

Blocked couplings not removable or demountable with hot press. For the coupled parts that must behave as a single piece, suitable to transmit high axial loads and torques.

For components that must move relative to one another with abundant mechanical play, generally with a rotary motion.

Running fits with greater clearances without any special requirements for fit accuracy.

For components which in all cases must be able to be assembled or disassembled by hand and for which, in spite of the large working tolerances, it is requested a possibly minimum play.

Couplings with discrete accuracy, with seat generally long, of mutually fixed parts, extractable by hand.

For components that must be disassembled very free respect to one another with abundant mechanical play: operating temperature much higher than the one at mounting.

Rotating parts with high precision, with low and heavy loads, lubricated rationally, with correct hydrodynamic sustenance.

Easily demountable parts, distance rings, parts of machines fixed to shafts using pins, bolts, rivets or welds.

Fixed plugs, driven bushings, armatures of electric motors on shafts, gear rims, flushed bolts.

Precision couplings, with seat generally short, of parts mutually fixed, extractable by hand. Ex .: Spare wheels mounted with keyways or splined shafts.

For components with very strong blocking, with disassembly practicable only by substitution of one of the components.

The following tables report the preferred metric fits and tolerances for hole and shaft basis systems given by the ISO 286-1 (2010) and ANSI B4.2-1978 standards. The use of these tolerances is advised for economic reasons.

Rotating parts with high precision, with low and heavy loads, lubricated rationally, with correct hydrodynamic sustenance.

Precision couplings, with seat generally short, of parts mutually fixed, extractable by hand. Ex .: Spare wheels mounted with keyways or splined shafts.

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Locational interference fit for parts requiring rigidity and alignment with prime accuracy of location but without special bore pressure requirements.

Blocked couplings, not disassembled by hand, to be secured against mutual rotation. Ex .: Fixed forced gears, mounted with keyways or on splined shafts, to dismantle very rarely.

Hi B Srinivasan, Tolerances are just tolerances applicabile for all fitting application. Of course if square section, the rotation capacity is assured in itself without an interference fit. The machining process for square section is of course different with respect to the same for circular. The fitting result between the realized elements is basically the same.

Ex .: Drawers and hydraulic taps. Shafts and transmission bushes rotating at low speed and subject to efforts of a limited entity.

The selection of a specific fit should take into account some aspects such as: constructional and technological views, economical aspects, measuring instruments, gauges and tools which are implemented in the production.

Ex .: Shaft and transmission bushes with a manual drive, without great importance. Idle pulleys.

Precision couplings, with seat generally short, of parts mutually fixed, extractable by hand.

Additional information about the standard fits that can be found in the practice are reported in the following tables for the Hole Basis and Shaft Basis systems respectively.

Ex .: Shafts and bushes in general. Ball bearings not very fast and not very loaded.

Force fit suitable for parts which can be highly stressed or for shrink fits where the heavy pressing forces required are impractical.

For components that must be disassembled very free respect to one another with abundant mechanical play: operating temperature much higher than the one at mounting.

Tight fits with small clearances or negligible interference. The parts can be assembled or disassembled manually.

For fixed members, with respect to each other, assembled and disassembled without big pressure. Parts secured against rotation and sliding.

Running fits with greater clearances without any special requirements for accuracy of guiding shafts.

Fixed fits with negligible clearances or small interferences. Mounting of fits using pressing and light force.

Similar fits with small clearances or small interferences. The parts can be assembled or disassembled without great force using a rubber mallet.

(*) This coupling is classified by all the texts as stable, even if it presents a minimum play for some combination of values between the shaft and the hole (shaft at min and hole at max).

For couplings slightly blocked, easily removable by hand, preferably for long seats to be secured against mutual rotation. Ex .: Fixed forced gears, mounted with keyways or on splined shafts, to dismantle very rarely.

Ex .: Oscillating levers moved by cams in bushing. Command pivots and positioning pins with high precision.

For components that must be disassembled very free respect to each other with abundant mechanical play: operating temperature much higher than the one at mounting.

For components that must be disassembled very free respect to one another with abundant mechanical play: operating temperature much higher than the one at mounting.

The following tables report some recommended fits for some applications. Of course the tables don’t pretend to be exhaustives and uniques.

For components that must be disassembled very free respect to each otherwith abundant mechanical play: operating temperature much higher than the one at mounting.

Multiple fits of shafts of production and piston machines, parts rotating very rarely or only swinging.

For fixed components with respect to each other, hardly removable by hand and secured against rotation and sliding.

For components that must move relative to each other with abundant mechanical play, generally with a rotary motion.

Easily dismountable fits of hubs of gears, pulleys and bushings, retaining rings, frequently removed bearing bushings.

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(*) This coupling is classified by all the texts as transition fit, although there is never play in any combination of values between the shaft and the hole.

Precision couplings, with seat generally short, of parts mutually fixed, extractable by hand. Parts to be secured against sliding and rotation.

Pressed fits with guaranteed interference. Assembly of the parts can be carried out using cold pressing.

Components fixed respect to each other, assembled and disassembled without excessive pressure and secured against rotation and sliding.

For components fixed with respect to each other, which can be mounted only by strong pressure; normally the two bodies are secured against rotation and sliding.

For fixed components with respect to each other, which can be easily assembled and disassembled, to be secured against mutual rotation.

Blocked couplings not removable or demountable with hot press. For the coupled parts that must be as a single piece, suitable to transmit high axial loads and torques.

For very fast rotating components, even with imperfect centering and sustenance not perfectly hydrodynamics and good mechanical play.

Main fits of machine tools. General fits of shafts, regulator bearings, machine tool spindles, sliding rods.

The aim is to help the designer to choose the appropriate and preferred fit tacking into account the standard uses for mechanical applications.

Ex .: Holes of hinges or pins for command by pin hand commands, bushings and sliding components without importance.

Rotating couplings with average peripheral speed (2-4 m/s), with need of limited plays. Couplings with alternate axial movement with medium and high speeds.