Selection and application of ISO dimensional tolerances – ANSI – UNI

Check a summary of the information available in the technical literature about adjustment tolerances between shafts and holes, aiming to provide guidance to the designer in choosing appropriate and preferred adjustments, especially considering common standards for mechanical applications

Calculation tools for dimensional tolerance selection

ISO and ANSI standards

to follow, tables containing metric fits and preferred tolerances for hole and shaft base systems are presented, as defined by ISO standards 286-1 (2010) is ANSI B4.2-1978. The adoption of these tolerances is recommended considering the economic aspects, providing a reference for design decisions in mechanical applications.

Preferred Settings Table (ANSI B4.2-1978)

Setting type	Furo base ISO	ISO base axis	Description
Clearance adjustments	H11/c11	C11/h11	Fits loosely to wide commercial tolerances or allowances on external members.
	H9/d9	D9/h9	Free play adjustment, not recommended when accuracy is essential, but suitable for large temperature variations, high operating speeds or high shaft pressures.
	H8/f7	F8/h7	Adjustment with reduced play, Suitable for operation on precise machines and precise location at moderate speeds and shaft pressures.
	H7/g6	G7/h6	Sliding adjustment not intended to function freely, but to move and rotate freely and locate accurately.
	H7/h6	H7/h6	Local clearance adjustment provides comfortable fit for locating stationary parts; but can be assembled and disassembled freely.
Transition adjustments	H7/k6	R7/h6	Locating clearance adjustment provides a tight fit for locating stationary parts; but can be assembled and disassembled freely.
	H7/n6	N7/h6	Transition from proper location to more precise location where greater interference is permitted.
Interference adjustments	H7/p6	P7/h6	Location interference adjustment for parts that require rigidity and alignment with excellent location accuracy, but no special internal pressure requirements.
	H7/s6	S7/h6	Medium fit for common steel parts or retractable fits on light sections, the tightest fit usable with cast iron.
	H7/u6	U7/h6	Force adjustment suitable for parts that can be highly stressed or for shrink adjustments where the strong pressing forces required are impractical.

Preferable system settings based on base hole (ISO 286-1:2010)

Open it

Tolerance classes for shafts

Base

Clearance adjustments

Transition adjustments

Interference adjustments

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

H8

d8

e8

f8

h8

H9

d8

e8

f8

h8

H10

b9

c9

d9

e9

h9

H11

b11

c11

d10

h10

Preferred base axis system settings (ISO 286-1:2010)

Tolerance classes for holes

Basic Axis

Clearance adjustments

Transition adjustments

Interference adjustments

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

h9

D9

E9

F9

H9

h9

B11

Q10

D10

H10

Note: For economic reasons, the first adjustment choice should, whenever possible, be made based on the tolerance classes highlighted above in azul. The tables below show the preferable tolerance zones for standard UNI couplings.

Recommended tolerance zone for shafts (UNI)

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

Recommended tolerance zone for holes (UNI)

Quality

A

B

C

CD

D

E

F

G

H

J.

JS

K

M

N

P

R

S

T

COM

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

#

Legend:

• "x":  General use, fine mechanical precision
• "o": General use only
• "#": Only fine mechanical precision

The following tables report some recommended settings for some applications. Please note that the tables are not intended to cover all applications and be the only indications.

Selecting a specific setting must take into account some aspects such as: constructive and technological conditions, economic aspects, measuring instruments and tools that are implemented in production.

In the tables below the preferred settings, as also defined by ANSI B4.2, are in azul.

Clearance adjustments (as per ANSI B4.2 highlighted)

ISO symbol	Description	applications
H11/a11 , H11/c11 , H11/c9, H11/d11, A11/h11, C11/h11 , D11/h11	Fits large gaps with parts with large tolerances.	Pivots, latches, fittings of parts exposed to corrosive effects, dust contamination and thermal or mechanical deformations.
H9/C9, H9/d10 , H9/d9 , H8/d9, H8/d8, D10/h9 , D9/h9 , D9/h8	The operation adjusts to larger clearances without any special accuracy requirements of the guide shafts.	Multiple adjustments of production shafts and piston machines, parts rotating very rarely or just oscillating.
H9/e9 , H8/e8 , H7/e7, E9/h9 , E8/h8, E8/h7	Execution fits with larger clearances without any special fit accuracy requirements.	Long stem adjustments, for example. in agricultural machinery, pump bearings, fans and piston machines.
H9/f8, H8/f8, H8/f7 , H7/f7 ,F8/h7 , F8/h6	Run fits with smaller clearances with general fit accuracy requirements.	Main machine tool adjustments. General axis adjustments, regulating bearings, machine tool spindles, sliding rods.
H8/g7, H7/g6 , G7/h6	Execution fits with very small gaps for precise axis orientation. No noticeable play after assembly.	Machine Tool Parts, sliding gears and clutch discs, crankshaft journals, pistons of hydraulic machines, sliding rods in bearings, grinding machine spindles.
H11/h11, H11/h9	Sliding adjustments of parts with large tolerances. Parts can be easily slid into each other and rotated.	Easily dismantled parts, spacer rings, machine parts fixed to shafts by means of pins, screws, rivets or welds.
H8/h9, H8/h8, H8/h7, H7/h6	Sliding adjustments with very small gaps for precise part orientation and centering. Sliding assembly without using great force, After lubrication, the parts can be rotated and slid manually.	Precise guidance of machines and preparations, interchangeable wheels, roller guides.

Transition Adjustments (as per ANSI B4.2 highlighted)

ISO symbol	Description	applications
H8/j7, H7/js6, H7/j6 , J7/h6	Tight fits with small gaps or negligible interference. Parts can be assembled or disassembled manually.	Easily detachable gear hub adjustments, pulleys and bushings, retaining rings, frequently removed bearing bushings.
H8/k7, H7/k6 , K8/h7, K7/h6	Similar fits with small gaps or small interferences. Parts can be assembled or disassembled without much force with a rubber mallet.	Detachable gear hub and pulley housings, hand wheels, clutches, brake discs.
H8/p7, H8/m7, H8/n7, H7/m6, H7/n6 , M8/h6, N8/h7, N7/h6	Fixed fits with negligible play or small interference. Pressure and light force fitting assembly.	Fixed plugs, driven bushings, electric motor armatures on shafts, gear rims, flush screws.

Interference Adjustments (as per ANSI B4.2 highlighted)

ISO symbol	Description	applications
H8/r7, H7/p6 , H7/r6 , P7/h6 , R7/h6	Pressed fits with guaranteed interference. The assembly of parts can be carried out by cold pressing.	Clutch disc hubs, bearing bushings.
H8/s7, H8/t7 , H7/s6 , H7/t6, S7/h6, T7/h6	Pressed fits with medium interference. Assembly of parts by hot pressing. Assembly by cold pressing only with the 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 adjustments with large interferences. Assembly by pressing and high forces at different part temperatures.	Permanent gear couplings with shafts, flanges.

Additional information about standard settings that may be encountered in practice is reported in the following tables for the Base Hole and Base Shaft systems, respectively.

Furo Base - Fit loosely

Setting type	Fit Specification	Assembly	applications
Clearance adjustments	H11 - a11	the hand	For components that must be dismantled very freely, respect each other with abundant mechanical clearance: operating temperature much higher than the assembly temperature.
Clearance adjustments	H10 - d8	the hand	For components that must be dismantled very freely, respect each other with abundant mechanical clearance: operating temperature much higher than the assembly temperature.
Clearance adjustments	H8-f8	the hand	For rotary couplings in general, with low loads and no need for fine centering. Ex.: Shaft and transmission bushings with manual drive, of no great importance.
Clearance adjustments	H7 - f6	the hand	For rotary couplings in general, with low loads and no need for fine centering. Ex.: Shaft and transmission bushings with manual drive, of no great importance. Idle pulleys.
Clearance adjustments	H6 - g5	the hand	High Precision Rotating Parts, with low and heavy loads, rationally lubricated, with correct hydrodynamic support. Ex.: Steel rotating shafts, hardened and ground bushings.
Clearance adjustments	H11 - b11	the hand	For components that must be dismantled very freely, respect each other with abundant mechanical clearance: operating temperature much higher than the assembly temperature.
Clearance adjustments	H8-e7	the hand	For components that must move relative to each other with abundant mechanical clearance, generally with rotary movement.
Clearance adjustments	H8 - f7	the hand	For rotary couplings in general, with low loads and no need for fine centering. Ex.: Shaft and transmission bushings with manual drive, of no great importance.
Clearance adjustments	H7-g7	the hand	For components that must move relative to each other, but without excessive slack.
Clearance adjustments	H13 - h11	the hand	For components which in all cases must be capable of being assembled or disassembled manually and for which, despite large working tolerances, possibly minimal time off is requested.
Clearance adjustments	H8 - h8	the hand	Axially Lubricated Slip Couplings, no need for precision, with long seat or low loads. Ex.: Hydraulic drawers and taps. Transmission shafts and bushings rotating at low speed and subject to stress from a limited entity.
Clearance adjustments	H6 - h6	the hand	For high-precision components that can move relative to each other in slow motion.
Clearance adjustments	H11 - c11	the hand	For components that must be dismantled very freely, respect each other with abundant mechanical clearance: operating temperature much higher than the assembly temperature.
Clearance adjustments	H9-f8	the hand	For components that must move relative to each other.
Clearance adjustments	H7 - f7	the hand	For very fast rotating components, even with imperfect centering and support, not perfectly hydrodynamic and with good mechanical clearance. Ex.: High speed axles, in general on your bushings. Pin positioning with medium accuracy.
Clearance adjustments	H7 - g6	the hand	Rotary couplings with medium peripheral speed (2-4 m/s), requiring limited time off. Ex.: Shafts and bushings in general. Ball bearings not too fast and not too loaded.
Clearance adjustments	H11 - h11	the hand	Axially sliding couplings, no need for precision. Ex.: Hinge holes or pins for control by manual pin controls, unimportant bushings and sliding components.
Clearance adjustments	H7 - h7	the hand	For components that can move if lubricated relative to each other, with slow motion.
Clearance adjustments	H6 - h5	the hand	For components with high axial sliding accuracy, or equipped with slow rotating or oscillatory movement, with internal lubrication. Ex.: Rocker levers driven by cams in bushings. Command pivots and positioning pins with high precision.

Furo Base - Transition adjustments

Setting type	Fit Specification	Assembly	applications
Transition adjustments	H7-j6	by light hammer blows	Discrete Precision Couplings, usually long thirsty, of mutually fixed parts, manually extractable.
Transition adjustments	H7-k6	by hammer	Couplings protected against mutual rotation by keys, pins, etc., easily removable. Ex.: ball bearings and roller bearings. braces. Joint fixing in general.
Transition adjustments	H7 - n6	Hammer, press or temperature difference	For slightly blocked couplings, easily removable manually, preferably for long seats protected against mutual rotation. Ex.: Fixed forced gears, mounted with keyways or on splined shafts, to disassemble very rarely.
Transition adjustments	H6-j6	by light hammer blows	Precision Couplings, usually short thirst, of parts fixed together, manually extractable. Ex.: Spare wheels mounted with keys or splined axles.
Transition adjustments	H6-k6	by hand with a lead hammer	Couplings protected against mutual rotation. Keyway couplings for high torques.
Transition adjustments	H6 - n6*	Hammer, press or temperature difference	For components fixed together, which can only be assembled using strong pressure; normally both parts must be protected against rotation and sliding. Ex.: Couplings without keyways for low torque transmission.
Transition adjustments	H6 - j5	by light hammer blows	Precision Couplings, usually short thirst, of parts fixed together, manually extractable. Ex.: Spare wheels mounted with keys or splined axles.
Transition adjustments	H6 - j5	by light hammer blows	Precision Couplings, usually short thirst, of parts fixed together, manually extractable. Ex.: Spare wheels mounted with keys or splined axles.
Transition adjustments	H7 - m6	Hammer, press or temperature difference	For mutually fixed components, assembled and dismantled manually or with little effort; fixed centering seats with good precision. Parts to be protected against rotation and sliding.
Transition adjustments	H6 - n5*	Hammer, press or temperature difference	Blocked couplings, not dismantled manually, to be protected against mutual rotation. Ex.: Fixed forced gears, mounted with keyways or on splined shafts, to disassemble very rarely.
(*) This coupling is classified by all texts as transition adjustment, although there is never play in any combination of values ​​between shaft and hole.

Furo Base - Interference adjustments

Setting type	Fit Specification	Assembly	applications
Interference adjustments	H7-p7	Hammer, press and/or temperature difference	Fixed components in relation to each other.
Interference adjustments	H7 - s6	Sledgehammer, press and temperature difference	Non-removable or detachable locking couplings with hot pressing. For mated parts that must behave as a single part, suitable for transmitting axial loads and torques without the use of keys or similar systems. Ex.: Bushings in your outer seat, never to be dismantled.
Interference adjustments	H6-p5	Hammer, press and/or temperature difference	Non-removable or detachable locking couplings with hot pressing. For mated parts that must behave as a single part, suitable for transmitting high axial loads and torques. Ex.: Bushings in your outer seat, never to be dismantled.
Interference adjustments	H7 - u7	Pressure and temperature difference	For components with very strong blockage, disassembly being practicable only by replacing one of the components. Ex.: Steel and bronze bushings in their seats and pins with movement organs.
Interference adjustments	H7 - r6	Sledgehammer, press and temperature difference	Non-removable or detachable locking couplings with hot pressing. For mated parts that must behave as a single part, suitable for transmitting axial loads and torques without the use of keys or similar systems. Ex.: Bushings in your outer seat, never to be dismantled.
Interference adjustments	H7 - u6	Pressure and temperature difference	For components with very strong blockage, disassembly being practicable only by replacing one of the components. Ex.: Steel and bronze bushings in their seats and pins with movement organs.

Base axis - Slack Adjustments

Setting type	Fit Specification	Assembly	applications
Clearance adjustments	A11 - h11	the hand	For components that must be dismantled very freely, respect each other with increased mechanical clearance: operating temperature much higher than the assembly temperature.
Clearance adjustments	D10 - h8	the hand	For components that must be dismantled very freely, respect each other with a lot of mechanical play: operating temperature much higher than the assembly temperature.
Clearance adjustments	F9-h8	the hand	For components that need to be disassembled, respect each other very freely, with increased mechanical clearance.
Clearance adjustments	F7-h7	the hand	For very fast rotating components, even with imperfect centering and support, not perfectly hydrodynamic and with good mechanical clearance.
Clearance adjustments	G7 - h6	the hand	Rotary couplings with medium peripheral speed (2-4 m/s), requiring limited time off. Couplings with alternating axial movement at medium and high speeds.
Clearance adjustments	B11 - h11	the hand	For components that must be dismantled very freely, respect each other with great mechanical clearance: operating temperature much higher than the assembly temperature.
Clearance adjustments	E9-h8	the hand	For components that need to be disassembled, respect each other very freely, with large mechanical clearance.
Clearance adjustments	F8-h8	the hand	For rotary couplings in general, with low loads and no need for fine centering.
Clearance adjustments	F7-h6	the hand	For rotary couplings in general, with low loads and no need for fine centering.
Clearance adjustments	G6 - h5	the hand	High Precision Rotating Parts, with low and heavy loads, rationally lubricated, with correct hydrodynamic support.
Clearance adjustments	C11 - h11	the hand	For components that must be dismantled very freely, respect each other with great mechanical clearance: operating temperature much higher than the assembly temperature.
Clearance adjustments	E8-h7	the hand	For components that must move relative to each other with increased mechanical clearance, generally with rotary movement.
Clearance adjustments	F8-h7	the hand	For components that must move relative to each other with tight clearance.
Clearance adjustments	G7 - h7	the hand	For components that must move relative to each other, but without excessive slack.

Base axis - Transition Adjustments

Setting type	Fit Specification	Assembly	applications
Transition adjustments	J7-h7	by hand or with light taps with a hammer	For components that should not slide too easily between each other, but which can be easily assembled and disassembled, protected against rotation and sliding.
Transition adjustments	J6 - h5	by light hammer blows	Precision Couplings, usually short thirst, of parts fixed together, manually extractable.
Transition adjustments	K7 - h6	Hammer or hand press	Fixed components removable with light pressure.
Transition adjustments	M6 - h6	Hammer, press or temperature difference	For fixed members, each other, assembled and disassembled without great pressure. Parts protected against rotation and sliding.
Transition adjustments	N7 - h6	Hammer, press or temperature difference	For slightly blocked couplings, difficult to remove manually, preferably for long seats and to be protected against mutual rotation.
Transition adjustments	J7-h6	by light hammer blows	Discrete Precision Couplings, usually long thirsty, of mutually fixed parts, manually extractable.
Transition adjustments	K8 - h7	by hand or with light taps with a hammer	Components fixed to each other, assembled and disassembled without excessive pressure and protected against rotation and sliding.
Transition adjustments	K6 - h6	by hammer	For components fixed together, which can be easily assembled and disassembled, to be protected against mutual rotation.
Transition adjustments	N8 - h7	Hammer, press or temperature difference	For components fixed together, difficult to remove manually and protected against rotation and sliding.
Transition adjustments	N6 - h7	Sledgehammer, press and temperature difference	For components fixed together, which can only be assembled using strong pressure; normally both bodies are protected against rotation and sliding.
Transition adjustments	J8-h7	by hand or with light taps with a hammer	For components that should not slide too easily between each other, but which can be easily assembled and disassembled, protected against rotation and sliding.
Transition adjustments	J6-h6	By light hammer blows	Precision Couplings, usually short thirst, of parts fixed together, manually extractable. Parts protected against sliding and rotation.
Transition adjustments	K7 - h7	Hammer or hand press	Components fixed to each other, assembled and disassembled without excessive pressure and protected against rotation and sliding.
Transition adjustments	M7 - h6	Hammer, press or temperature difference	Components fixed together, assembled and disassembled manually or with little effort; fixed centering seats with good precision. Parts to be assembled against rotation and sliding.
Transition adjustments	N7 - h7	Hammer, press or temperature difference	Components fixed together and protected against rotation and sliding.
Transition adjustments	N6 - h5*	Sledgehammer, press and temperature difference	Blocked couplings, not dismantled manually, to be protected against mutual rotation.
(*) This coupling is classified in the bibliography as transition adjustment, although there is never play in any combination of values ​​between shaft and hole.

Base axis - Interference Adjustments

Setting type	Fit Specification	Assembly	applications
Interference adjustments	P7 - h7*	Sledgehammer, press and temperature difference	Components fixed to each other.
Interference adjustments	R7 - h6	Sledgehammer, press and temperature difference	Non-removable or detachable locking couplings with hot pressing. For parts coupled as a single part, suitable for transmitting axial loads and torques without the use of keys or similar systems.
Interference adjustments	P6 - h5	Sledgehammer, press and temperature difference (heating or cooling)	Non-removable or detachable locking couplings with hot pressing. For parts coupled as a single part, suitable for transmitting high axial loads and torques.
Interference adjustments	S7 - h6	Pressure and temperature difference (heating or cooling)	Non-removable or detachable locking couplings with hot pressing. For parts coupled as a single part, suitable for transmitting axial loads and torques without the use of keys or similar systems.
Interference adjustments	R8 - h7	Sledgehammer, press and temperature difference (heating or cooling)	For members fixed to each other.
(*) This coupling is classified by all texts as stable, even if it presents minimum clearance for some combination of values ​​between the shaft and the hole (axis at minimum and hole at maximum).

Credits: https://www.mec-engineering-spreadsheets.com/documentation-area/fit-tolerances-and-applications