ISO Fits & Tolerances Chart (ISO 286)

ISO 286 hole and shaft fit designations with clearance, transition and interference classes plus IT grade tolerance values.

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ISO 286 describes a fit by pairing a hole tolerance (upper-case letter) with a shaft tolerance (lower-case letter), each followed by an IT grade number that sets the tolerance width. H7/g6 is a running clearance fit; H7/p6 is a light press fit. This chart lists the standard hole-basis fits with their function and typical applications, and gives IT grade tolerance widths in micrometres for common nominal size ranges.

Hole-basis fits (ISO 286-2)

Hole basis keeps the hole tolerance fixed at H and varies the shaft, which suits production where holes are made with standard reamers.

Fit	Type	Character	Typical application
H11/c11	Clearance	Very loose running	Agricultural machinery, wide clearance pivots, coarse assemblies
H9/d9	Clearance	Loose running	Large clearance bearings, exposed shafts, high temperature
H8/f7	Clearance	Close running	Sleeve bearings with good lubrication, gearbox shafts
H7/g6	Clearance	Sliding	Precision sliding parts, spigots, accurate location with free movement
H7/h6	Clearance	Locational clearance	Parts that must assemble freely but locate accurately
H7/j6	Transition	Push fit	Easily dismantled location, light tapping to assemble
H7/k6	Transition	Light keying fit	Bearing inner rings on shafts, gears and pulleys with keys
H7/n6	Transition	Tight keying fit	Permanent-ish location requiring press assembly
H7/p6	Interference	Light press fit	Locating dowels, bushes pressed into housings
H7/r6	Interference	Medium press fit	Shrink-fitted collars and gears in steel
H7/s6	Interference	Heavy press fit	Permanent assemblies, torque transmitted by friction
H7/u6	Interference	Force fit	Heavy shrink fits, railway wheel seats

12 rows

IT grade tolerance values (µm)

Values from the ISO 286-1 standard tolerance table. The grades run from IT01 to IT18 and widen with nominal size. IT6 and IT7 cover most machined precision work; IT11 and above suit as-cast or as-sawn features. Size bands are "over" the lower figure, up to and including the upper one, so 10 mm sits in the 6 to 10 band.

Nominal size (mm)	IT4	IT5	IT6	IT7	IT8	IT9	IT10	IT11	IT12
Up to 3	3	4	6	10	14	25	40	60	100
Over 3 to 6	4	5	8	12	18	30	48	75	120
Over 6 to 10	4	6	9	15	22	36	58	90	150
Over 10 to 18	5	8	11	18	27	43	70	110	180
Over 18 to 30	6	9	13	21	33	52	84	130	210
Over 30 to 50	7	11	16	25	39	62	100	160	250
Over 50 to 80	8	13	19	30	46	74	120	190	300
Over 80 to 120	10	15	22	35	54	87	140	220	350
Over 120 to 180	12	18	25	40	63	100	160	250	400
Over 180 to 250	14	20	29	46	72	115	185	290	460
Over 250 to 315	16	23	32	52	81	130	210	320	520
Over 315 to 400	18	25	36	57	89	140	230	360	570
Over 400 to 500	20	27	40	63	97	155	250	400	630

13 rows

Common precision-fit tolerance examples

Nominal size	H7 hole (mm)	g6 shaft (mm)	k6 shaft (mm)	p6 shaft (mm)
10 mm	+0.015 / 0	−0.005 / −0.014	+0.010 / +0.001	+0.024 / +0.015
20 mm	+0.021 / 0	−0.007 / −0.020	+0.015 / +0.002	+0.035 / +0.022
30 mm	+0.021 / 0	−0.007 / −0.020	+0.015 / +0.002	+0.035 / +0.022
50 mm	+0.025 / 0	−0.009 / −0.025	+0.018 / +0.002	+0.042 / +0.026
80 mm	+0.030 / 0	−0.010 / −0.029	+0.021 / +0.002	+0.051 / +0.032
120 mm	+0.035 / 0	−0.012 / −0.034	+0.025 / +0.003	+0.059 / +0.037

6 rows

About the ISO Fits & Tolerances Chart

Sources

Classification: Standard fit and tolerance designations

Sources

ISO 286-1 — Geometrical product specifications (GPS) — Tolerance grades
ISO
ISO 286-2 — GPS — Tables of standard tolerance grades and limit deviations
ISO

Hole-basis and shaft-basis fit designations (e.g. H7/g6) and the clearance/transition/interference classes are defined by ISO 286. The designation encodes a fundamental deviation letter and an IT tolerance grade; the actual limit deviations are looked up per nominal size in ISO 286-2.

How it was compiled

A fit is the relationship between a hole and shaft tolerance zone. ISO 286 defines the tolerance grades (IT) and fundamental deviations (letters); combining a hole and shaft designation gives a clearance, transition, or interference fit. The hole-basis system (H…) is most common because holes are harder to machine to size.

How current it is

Classification: Stable (mature standard)

The ISO 286 fit system has been stable for decades. Confirm the current edition for procurement and inspection, especially for the limit-deviation tables.

Limitations

The designation defines the fit class; the actual limit deviations must be looked up per nominal size in ISO 286-2.
Fits assume standard temperature (20 °C); thermal expansion shifts the fit at operating temperature.
Geometric tolerances (roundness, cylindricity) are separate from the size tolerance and can affect the real fit.

Using it

Use the hole-basis system (H…) by default; switch to shaft-basis only when the shaft is the fixed element.
Look up the actual limit deviations for the nominal size in ISO 286-2 before specifying on a drawing.
Account for thermal expansion and geometric tolerances when the fit is temperature- or form-critical.

Units and notation

Limit deviations and tolerance values in micrometres (µm) for the size ranges shown.

Frequently Asked Questions

What does H7/g6 mean?

H7 is the hole tolerance: grade 7 width with its lower limit at the nominal size. g6 is the shaft: grade 6 width positioned slightly below nominal. Together they always leave a small clearance, giving a precise sliding fit.

What is the difference between hole basis and shaft basis?

Hole basis fixes the hole at H and varies the shaft; shaft basis fixes the shaft at h and varies the hole. Hole basis is preferred because standard reamers and bearings set the hole size.

Which fit should I use for a ball bearing on a shaft?

A rotating inner ring under normal load typically uses k6 (or j6 for light loads), with the housing bore at H7. Always confirm against the bearing manufacturer table for your load case.

What are IT grades?

International Tolerance grades define the width of a tolerance zone as a function of nominal size. Lower numbers are tighter: IT6 on a 20 mm feature is 13 µm wide, IT12 is 210 µm.

How do I convert a fit into actual limits?

Take the IT grade width for the size range and apply the fundamental deviation of the letter. For a 20 mm H7 hole that gives +0.021 / 0 mm, so limits of 20.000 and 20.021 mm.

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