ISO 286 Fits and Tolerances — H7, g6, k6 and the Common Fit Pairs (with Tables)

Dimensional reference compiled by cBallast. 3-page PDF; the full content is on this page.

Compiled by

cBallast

Subject

Machining fits

Document type

Dimensional reference

Reference

2026 edition

Issued

2026-10-04

Pages

Format

Web page and PDF

IT tolerance values for IT6–IT11 by size range, what H7/g6, H7/k6, H7/p6 and other common ISO 286 fit pairs mean in practice, and clearance/interference numbers for the shaft-and-hole sizes used in bearings, bushings and couplings.

The system in one paragraph

ISO 286 describes a limit-and-fit system: a letter positions the tolerance zone relative to the nominal size (capital letters for holes, lower-case for shafts; H starts exactly at nominal and goes plus, h goes minus; letters before h/H give clearance, after give interference) and the IT number gives the width of the zone. Most machine design is hole-basis: the hole is H7 and the shaft letter chooses the fit.

IT grade values (µm)

Over–incl. (mm)	IT6	IT7	IT8	IT9	IT11
3–6	8	12	18	30	75
6–10	9	15	22	36	90
10–18	11	18	27	43	110
18–30	13	21	33	52	130
30–50	16	25	39	62	160
50–80	19	30	46	74	190
80–120	22	35	54	87	220
120–180	25	40	63	100	250

Common fit pairs and what they do

Fit	Character	Typical use	Ø25 example (µm)
H7/g6	Close running clearance	Bushes, sliding spindles, drylin liners	+7 … +41 clearance
H7/h6	Locational clearance	Spigots, covers, light press-by-hand	0 … +34 clearance
H7/k6	Light transition	Ball-bearing inner rings on shafts, pulleys	−15 … +19
H7/n6	Firm transition	Gears, couplings that must not fret	−28 … +6
H7/p6	Light interference (press)	Bearing bushes in housings, dowel seats	−35 … −1 interference
H7/s6	Heavy interference (shrink)	Permanent hubs, valve-seat rings	−56 … −22 interference

Example read-out, Ø25 H7/g6: the hole is 25.000/25.021, the shaft 24.980/24.993, so the assembly always slides with 7–41 µm clearance. Rolling-bearing seats have their own convention — rotating-load rings sit on k6/m6 shafts and stationary rings in H7/J7 housings; dimensions for the bearings themselves are in the deep-groove bearing chart (e.g. SKF 6205 ETN9), and plain-bearing shafts for polymer bushings follow h6–h9 as described by igus for its drylin ranges.

Measuring to grade

Verifying IT6–IT7 work needs instruments an order of magnitude finer than the tolerance: a 1 µm-reading bore gauge or micrometer for Ø25 H7 (21 µm zone). Digital calipers (±20–30 µm) only screen IT11 and coarser — see measuring and assembly tools and the calibration-class guide for tool accuracy classes.

Frequently asked questions

What is the tolerance of a 25 mm H7 hole?: Ø25 H7 means +0/+21 µm: the hole must measure between 25.000 and 25.021 mm.
What fit is H7/g6?: A close running clearance fit — the shaft is always smaller than the hole by 7–41 µm at Ø25, suitable for bushes and sliding parts.
Which shaft tolerance for a ball-bearing seat?: For a rotating shaft load, k6 is the standard seat for small and medium deep-groove bearings (m6 for heavier duty); the housing is usually H7 when the outer ring is stationary.
What is the difference between H7 and h7?: Capital H is a hole zone starting at nominal and going plus; lower-case h is a shaft zone starting at nominal and going minus. Ø20 H7 = 20.000/20.021; Ø20 h7 = 19.979/20.000.
Is H7/p6 a press fit?: Yes — a light interference fit of roughly 1–35 µm at Ø25, assembled with a press or thermal differential, used for bushes and dowel seats.

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Reference compiled for identification and cross-reference. Dimensions are nominal; confirm against the controlling Multiple 2026 edition revision and the specific component data sheets before manufacture or procurement. All trademarks are the property of their respective owners.