This section reports a summary of the available information that can be found on technical literatureabout the fit tolerance between shafts and holes.The aim is to help the designer to choose the appropriate and preferred fit tacking into account thestandard uses for mechanical applications.ISO and ANSI StandardsThe following tables report the preferred metric fits and tolerances for hole and shaft basis systemsgiven by the ISO 286-1 (2010) and ANSI B4.2-1978 standards. The use of these tolerances is advised for economic reasons. Transitionfits:ISO SymbolDescriptionApplicationsH8/j7,H7/js6, H7/j6, J7/h6Tight fits with smallclearances or negligible interference. The parts can be assembled or disassembled manually.Easily dismountable fitsof hubs of gears, pulleys and bushings, retaining rings, frequently removed bearing bushings.H8/k7, H7/k6, K8/h7, K7/h6Similar fits with smallclearances or small interferences. The parts can be assembled or disassembled without great force using a rubber mallet.Demountable fits of hubsof gears and pulleys, manual wheels, clutches, brake disks.H8/p7, H8/m7, H8/n7,H7/m6, H7/n6, M8/h6, N8/h7, N7/h6Fixed fits withnegligible clearances or small interferences. Mounting of fits using pressing and light force.Fixed plugs, drivenbushings, armatures of electric motors on shafts, gear rims, flushed bolts. Interference fits:ISO SymbolDescriptionApplicationsH8/r7, H7/p6, H7/r6, P7/h6, R7/h6Pressed fits withguaranteed interference.
Assembly of the parts can be carried out using cold pressing.Hubs of clutch disks,bearing bushings.H8/s7,H8/t7, H7/s6, H7/t6, S7/h6, T7/h6Pressed fits with mediuminterference. Assembly of parts using hot pressing. Assembly using cold pressing only with use of large forces.Permanent coupling ofgears with shafts, bearing bushings.H8/u8, H8/u7,H8/x8, H7/u6, U8/h7,U7/h6Pressed fits with biginterferences.
Metric Fits And Tolerances Chart
Assembly using pressing and great forces under different temperatures of the parts.Permanent couplings ofgears with shafts, flanges. Type of fitFitsAssemblingApplicationsTransitionFitsH7- j6by light taps of malletCouplings with discrete accuracy, with seat generally long, of mutually fixed parts, extractable by hand.TransitionFitsH7- k6bymalletCouplings secured against mutual rotation by keyways, pins, etc., easily removable.Ex.: keying of ball bearings and roller bearings. Fixing joints in general.TransitionFitsH7- n6Mallet, press or temperature differenceFor 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.TransitionFitsH6- j6by light taps of malletPrecision couplings, with seat generally short, of parts mutually fixed, extractable by hand. Ex.: Spare wheels mounted with keyways or splined shafts.TransitionFitsH6- k6by hand with a lead hammerCouplings secured against mutual rotation. Couplings by keyways for high torques.TransitionFitsH6- n6.Mallet, press or temperature differenceFor components fixed respect to one another, which can be mounted only by strong pressure; normally the two parts must be secured against rotationand sliding. Ex.:Couplings without keyways to transmit low torques.TransitionFitsH6- j5by light taps of malletPrecision couplings, with seat generally short, of parts mutually fixed, extractable by hand.
Ex.: Spare wheels mounted with keyways or splined shafts.TransitionFitsH6- j5by light taps of malletPrecision couplings, with seat generally short, of parts mutually fixed, extractable by hand. Ex.: Spare wheels mounted with keyways or splined shafts.TransitionFitsH7- m6Mallet, press or temperature differenceFor components mutually fixed, assembled and demontable by hand or with little effort; fixed centering seats with good precision. Partsto be secured against rotation and sliding.TransitionFitsH6- n5.Mallet, press or temperature differenceBlocked 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.(.) This coupling is classified by allthe texts as transition fit, although there is never play in any combination of values between the shaft and the hole. Type of fitFitsAssemblingApplicationsInterference FitsH7 - p7Mallet,press and/or temperature differenceComponentsfixed respect to each other.Interference FitsH7 - s6Mallet,press and temperature differenceBlockedcouplings not removable or demountable with hot press.
Iso Tolerance Chart
For the coupled parts that must behave as a single piece, suitable to transmit axial loads and torqueswithout the use of keys or similar systems.Ex.: Bushesin their external seat, to be never dismounted.Interference FitsH6 - p5Mallet,press and/or temperature differenceBlockedcouplings not removable or demountable with hot press. For the coupled parts that must behave as a single piece, suitable to transmit high axial loads andtorques.Ex.: Bushesin their external seat, to be never dismounted.Interference FitsH7 - u7Press and temperature differenceForcomponents with very strong blocking, with disassembly practicable only by substitution of one of the components.Ex.: Steeland bronze bushings in their seats and pins with organs of motion.Interference FitsH7 - r6Mallet,press and temperature differenceBlockedcouplings not removable or demountable with hot press. For the coupled parts that must behave as a single piece, suitable to transmit axial loads and torqueswithout the use of keys or similar systems.Ex.: Bushesin their external seat, to be never dismounted.Interference FitsH7 - u6Press and temperature differenceForcomponents with very strong blocking, with disassembly practicable only by substitution of one of the components.Ex.: Steeland bronze bushings in their seats and pins with organs of motion.
Standard Tolerance Chart
Typeof fitFitsAssemblingApplicationsInterferenceFitsP7- h7.Mallet, press and temperature differenceComponents fixed respect to each other.InterferenceFitsR7- h6Mallet, press and temperature differenceBlocked couplings not removable or demountable with hot press. For the coupled parts that must behave as a single piece, suitable to transmitaxial loads and torques without the use of keys or similar systems.InterferenceFitsP6- h5Mallet, press and temperature differenceBlocked couplings not removable or demountable with hot press. For the coupled parts that must behave as a single piece, suitable to transmit highaxial loads and torques.InterferenceFitsS7- h6Pressand temperature differenceBlocked couplings not removable or demountable with hot press. For the coupled parts that must behave as a single piece, suitable to transmitaxial loads and torques without the use of keys or similar systems.InterferenceFitsR8- h7Mallet, press and temperature differenceFor fixed members respect to one another.(.) This coupling is classified by allthe 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).