Fit tolerances and applications


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

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

 

ISO and ANSI Standards

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.

 

ISO Symbol

Description

Hole Basis

Shaft Basis

Clearance Fits

H11/c11

C11/h11

Loose running fit for wide commercial tolerances or allowances on external members.

H9/d9

D9/h9

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

H8/f7

F8/h7

Close running fit for running on accurate machines and for accurate location at moderate speeds and journal pressures.

H7/g6

G7/h6

Sliding fit not intended to run freely, but to move and turn freely and locate accurately.

H7/h6

H7/h6

Locational clearance fit provides snug fit for locating stationary parts; but can be freely assembled and disassembled.

Transition Fits

H7/k6

K7/h6

Locational transition fit for accurate location, a compromise between clearance and interference.

H7/n6

N7/h6

Locational transition fit for more accurate location where greater interference is permissible.

Interference Fits

H7/p6

P7/h6

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

H7/s6

S7/h6

Medium drive fit for ordinary steel parts or shrink fits on light sections, the tightest fit usable with cast iron.

H7/u6

U7/h6

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

Preferred fits table (ANSI B4.2-1978)

 

Basic
Hole

Tolerance classes for shafts

Clearance Fits

Transition Fits

Interference Fits

H6

 

 

 

 

 

g5

h5

js5

k5

m5

 

n5

p5

 

 

 

 

 

H7

 

 

 

 

f6 

g6

h6

js6

k6

m6

n6

 

p6

r6

s6

t6

u6

x6

H8

 

 

 

e7

f7

 

h7

js7

k7

m7

 

 

 

 

s7

 

u7

 

 

 

d8

e8

f8

 

h8

 

 

 

 

 

 

 

 

 

 

 

H9

 

 

d8

e8

f8

 

h8

 

 

 

 

 

 

 

 

 

 

 

H10

b9

c9

d9

e9

 

 

h9

 

 

 

 

 

 

 

 

 

 

 

H11

b11

c11

d10

 

 

 

h10

 

 

 

 

 

 

 

 

 

 

 

Preferable fits of the hole-basis system (ISO 286-1:2010)

 

Basic
Shaft

Tolerance classes for holes

Clearance Fits

Transition Fits

Interference Fits

h5

 

 

 

 

 

G6

H6

JS6

K6

M6

 

N6

P6

 

 

 

 

 

h6

 

 

 

 

F7

G7

H7

JS7

K7

M7

N7

 

P7

R7

S7

T7

U7

X7

h7

 

 

 

E8

F8

 

H8

 

 

 

 

 

 

 

 

 

 

 

h8

 

 

D9

E9

F9

 

H9

 

 

 

 

 

 

 

 

 

 

 

h9

 

 

 

E8

F8

 

H8

 

 

 

 

 

 

 

 

 

 

 

 

 

D9

E9

F9

 

H9

 

 

 

 

 

 

 

 

 

 

 

B11

C10

D10

 

 

 

H10

 

 

 

 

 

 

 

 

 

 

 

Preferable fits of the shaft-basis system (ISO 286-1:2010)

 

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

 

 

The tables below report the preferable zones of tolerance for standard couplings from the UNI norms.

 

ZONE OF TOLERANCE RECOMMENDED FOR SHAFTS

 

Quality

a

b

c

d

e

f

g

h

j

js

k

m

n

p

r

s

t

u

x

5

 

 

 

 

 

 

x

x

x

x

x

x

x

x

x

x

o

 

 

6

 

 

 

 

 

x

x

x

x

x

x

x

x

x

x

x

o

x

 

7

 

 

 

 

x

x

x

x

x

x

x

x

x

x

x

x

o

x

x

8

 

 

 

x

x

x

 

x

 

 

 

 

 

 

 

 

 

 

 

9

x

x

 

x

x

 

 

x

 

 

 

 

 

 

 

 

 

 

 

10

 

 

 

x

 

 

 

x

 

 

 

 

 

 

 

 

 

 

 

11

o

o

o

 

 

 

 

x

 

 

 

 

 

 

 

 

 

 

 

 

ZONE OF TOLERANCE RECOMMENDED FOR HOLES

 

Quality

A

B

C

CD

D

E

F

G

H

J

JS

K

M

N

P

R

S

T

Z

ZB

ZC

6

 

 

 

 

 

 

x

x

x

x

x

x

x

x

x

x

x

o

 

 

 

7

 

 

 

 

 

 

x

x

x

x

x

x

x

x

x

x

x

o

 

 

 

8

 

 

 

 

 

x

x

 

x

x

x

x

x

x

x

x

 

 

x

 

 

9

 

 

 

·

x

x

x

 

x

 

x

 

 

 

 

 

 

 

 

x

x

10

 

 

 

·

x

x

 

 

x

 

 

 

 

 

 

 

 

 

 

 

 

11

o

o

x

·

x

 

 

 

x

 

 

 

 

 

 

 

 

 

 

 

 

13

 

·

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Legenda:

x general use, fine mechanical precision, watchmaking

o only general use

• only fine mechanical precision, watchmaking

 

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

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.

 

In the tables the preferred fits, as defined also by the ANSI B4.2, are in bold

 

Clearance fits:


ISO Symbol

Description

Applications

H11/a11, H11/c11, H11/c9, H11/d11, A11/h11, C11/h11, D11/h11

Fits with great clearances with parts having great tolerances.

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

H9/C9, H9/d10, H9/d9, H8/d9, H8/d8, D10/h9, D9/h9, D9/h8

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

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

H9/e9, H8/e8, H7/e7, E9/h9, E8/h8, E8/h7

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

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

H9/f8, H8/f8, H8/f7, H7/f7, F8/h7, F8/h6

Running fits with smaller clearances with general requirements for fit accuracy. 

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

H8/g7, H7/g6, G7/h6

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

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

H11/h11, H11/h9

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

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

H8/h9, H8/h8, H8/h7, H7/h6

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. 

Precise guiding of machines and preparations, exchangeable wheels, roller guides. 

 

Transition fits:

ISO Symbol

Description

Applications

H8/j7, H7/js6, H7/j6, J7/h6

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

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

H8/k7, H7/k6, K8/h7, K7/h6

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

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

H8/p7, H8/m7, H8/n7, H7/m6, H7/n6, M8/h6, N8/h7, N7/h6

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

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

 

Interference fits:

ISO Symbol

Description

Applications

H8/r7, H7/p6, H7/r6, P7/h6, R7/h6

Pressed fits with guaranteed 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/h6

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

Permanent coupling of gears with shafts, bearing bushings.

H8/u8, H8/u7, H8/x8, H7/u6, U8/h7, U7/h6

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

Permanent couplings of gears with shafts, flanges. 

 

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 system respectively.

 HOLE BASIS

 

Type of fit

Fits

Assembling

Applications

Clearance Fits

H11 - a11

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.

Clearance Fits

H10 - d8

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.

Clearance Fits

H8 - f8

by hand

For general rotating couplings, with low loads and without needs of fine centering.

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

Clearance Fits

H7 - f6

by hand

For general rotating couplings, with low loads and without needs of fine centering.

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

Clearance Fits

H6 - g5

by hand

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

Ex .: Rotating steel shafts, hardened and ground bushings.

Clearance Fits

H11 - b11

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.

Clearance Fits

H8 - e7

by hand

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

Clearance Fits

H8 - f7

by hand

For general rotating couplings, with low loads and without needs of fine centering.

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

Clearance Fits

H7 - g7

by hand

For components which must move relative to one another, but without excessive play.

Clearance Fits

H13 - h11

by hand

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.

Clearance Fits

H8 - h8

by hand

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

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

Clearance Fits

H6 - h6

by hand

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

Clearance Fits

H11 - c11

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.

Clearance Fits

H9 - f8

by hand

For components which must move relative to one another.

Clearance Fits

H7 - f7

by hand

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

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

Clearance Fits

H7 - g6

by hand

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

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

Clearance Fits

H11 - h11

by hand

Couplings sliding axially, without needs of pecision.

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

Clearance Fits

H7 - h7

by hand

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

Clearance Fits

H6 - h5

by hand

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

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

 

Type of fit

Fits

Assembling

Applications

Transition Fits

H7 - j6

by light taps of mallet

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

Transition Fits

H7 - k6

by mallet

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

Transition Fits

H7 - n6

Mallet, press or temperature difference

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.

Transition Fits

H6 - j6

by light taps of mallet

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

Transition Fits

H6 - k6

by hand with a lead hammer

Couplings secured against mutual rotation. Couplings by keyways for high torques.

Transition Fits

H6 - n6*

Mallet, press or temperature difference

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.

Transition Fits

H6 - j5

by light taps of mallet

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

Transition Fits

H6 - j5

by light taps of mallet

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

Transition Fits

H7 - m6

Mallet, press or temperature difference

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.

Transition Fits

H6 - n5*

Mallet, press or temperature difference

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.

(*) 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.

 

Type of fit

Fits

Assembling

Applications

Interference Fits

H7 - p7

Mallet, press and/or temperature difference

Components fixed respect to each other.

Interference Fits

H7 - s6

Mallet, press and temperature difference

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.

Ex .: Bushes in their external seat, to be never dismounted.

Interference Fits

H6 - p5

Mallet, press and/or temperature difference

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.

Ex .: Bushes in their external seat, to be never dismounted.

Interference Fits

H7 - u7

Press and temperature difference

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

Ex .: Steel and bronze bushings in their seats and pins with organs of motion.

Interference Fits

H7 - r6

Mallet, press and temperature difference

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.

Ex .: Bushes in their external seat, to be never dismounted.

Interference Fits

H7 - u6

Press and temperature difference

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

Ex .: Steel and bronze bushings in their seats and pins with organs of motion.

 

SHAFT BASIS


Type of fit

Fits

Assembling

Applications

Clearance Fits

A11 - h11

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.

Clearance Fits

D10 - h8

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.

Clearance Fits

F9 - h8

by hand

For components that have to be disassembled very free respect to one another with abundant mechanical play.

Clearance Fits

F7 - h7

by hand

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

Clearance Fits

G7 - h6

by hand

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.

Clearance Fits

B11 - h11

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.

Clearance Fits

E9 - h8

by hand

For components that have to be disassembled very free respect to one another with abundant mechanical play.

Clearance Fits

F8 - h8

by hand

For general rotating couplings, with low loads and without needs of fine centering.

Clearance Fits

F7 - h6

by hand

For general rotating couplings, with low loads and without needs of fine centering.

Clearance Fits

G6 - h5

by hand

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

Clearance Fits

C11 - h11

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.

Clearance Fits

E8 - h7

by hand

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

Clearance Fits

F8 - h7

by hand

For components which must move relative to one another with sensible play.

Clearance Fits

G7 - h7

by hand

For components which must move relative to one another, but without excessive play.

 

Type of fit

Fits

Assembling

Applications

Transition Fits

J7 - h7

by hand or by light taps of mallet

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

Transition Fits

J6 - h5

by light taps of mallet

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

Transition Fits

K7 - h6

Mallet or hand press

Fixed components removable with light pressure.

Transition Fits

M6 - h6

Mallet, press or temperature difference

For fixed members, respect to one another, assembled and disassembled without big pressure. Parts secured against rotation and sliding.

Transition Fits

N7 - h6

Mallet, press or temperature difference

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

Transition Fits

J7 - h6

by light taps of mallet

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

Transition Fits

K8 - h7

by hand or by light taps of mallet

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

Transition Fits

K6 - h6

by mallet

For components fixed respect to one another, which can be easily assembled and disassembled, to be secured against mutual rotation.

Transition Fits

N8 - h7

Mallet, press or temperature difference

For components fixed respect to one another, hardly removable by hand and secured against rotation and sliding.

Transition Fits

N6 - h7

Mallet, press and temperature difference

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

Transition Fits

J8 - h7

by hand or by light taps of mallet

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.

Transition Fits

J6 - h6

by light taps of mallet

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

Transition Fits

K7 - h7

Mallet or hand press

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

Transition Fits

M7 - h6

Mallet, press or temperature difference

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.

Transition Fits

N7 - h7

Mallet, press or temperature difference

Components fixed respect to each other and secured against rotation and sliding.

Transition Fits

N6 - h5*

Mallet, press and temperature difference

Blocked couplings, not disassembled by hand, to be secured against mutual rotation.

(*) 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.

 

Type of fit

Fits

Assembling

Applications

Interference Fits

P7 - h7*

Mallet, press and temperature difference

Components fixed respect to each other.

Interference Fits

R7 - h6

Mallet, press and temperature difference

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.

Interference Fits

P6 - h5

Mallet, press and temperature difference

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.

Interference Fits

S7 - h6

Press and temperature difference

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.

Interference Fits

R8 - h7

Mallet, press and temperature difference

For fixed members respect to one another.

(*) 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).

Your comments


Comments: 3
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  • #1

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