Verified by Rachel Mayfield, Supply Chain Analyst - June 2026
Photo by Dithira Hettiarachchi on Pexels
ISO 286 hole-basis fits for shafts and holes, with the common H7-based fit classes and what each is for. ISO Tolerance and Fits Chart (H7, h6, etc.) In the hole-basis system the hole is held to one tolerance (H7 is the standard) and the shaft tolerance is changed to set the fit - a clearance fit for sliding, a transition fit for accurate location, or an interference fit for a permanent press. H7/g6 slides freely; H7/p6 is a press fit.
| Fit (hole/shaft) |
Type |
Typical use |
| H7/g6 |
Clearance (sliding) |
Precise location with free movement - spigots, guide bushes, sliding parts |
| H7/h6 |
Clearance (location/slip) |
Easy hand assembly, accurate location - gears and pulleys on shafts |
| H7/k6 |
Transition |
Accurate location with slight grip, removable with a mallet - couplings, pulleys |
| H7/n6 |
Transition (tight) |
Accurate location needing light press - bushes, gears for heavier duty |
| H7/p6 |
Interference (press) |
Permanent location pressed together - bushes into housings, dowels |
| H7/s6 |
Interference (shrink) |
High-load permanent fit, often shrink-fitted - rings and collars on shafts |
| H11/c11 |
Coarse clearance |
Loose running fit for rough work - pivots, agricultural linkages |
How to read an ISO fit
A fit is written as hole tolerance over shaft tolerance, for example H7/g6. The capital letter is the hole, the lower-case letter is the shaft. The number is the tolerance grade (IT grade) - a smaller number is a tighter band. For a given diameter range the standard gives the exact upper and lower limits in micrometres.
Example: 18 to 30 mm diameter
| Tolerance (18-30 mm dia) |
Upper limit (µm) |
Lower limit (µm) |
| H7 (hole) |
+21 |
0 |
| g6 (shaft) |
-7 |
-20 |
| h6 (shaft) |
0 |
-13 |
| k6 (shaft) |
+15 |
+2 |
| p6 (shaft) |
+35 |
+22 |
| s6 (shaft) |
+48 |
+35 |
For a 25 mm shaft in an H7/g6 sliding fit, the hole is 25.000 to 25.021 mm and the shaft is 24.980 to 24.993 mm, giving a guaranteed clearance of 7 to 41 micrometres. Tolerances widen with diameter, so always read the band for the actual size range, not a single value.
Related standards
- ISO 286-1 - System of limits and fits, bases of tolerances
- ISO 286-2 - Tables of standard tolerance grades and limit deviations
- BS EN ISO 286 - UK implementation
Frequently Asked Questions
What is an H7 tolerance?
H7 is the standard hole tolerance in the ISO 286 hole-basis system. The lower limit is the nominal size (zero deviation) and the upper limit is positive, so an H7 hole is always at or above nominal. For an 18 to 30 mm diameter, H7 is +0.021/0 mm, meaning a 25 mm H7 hole measures 25.000 to 25.021 mm.
What is the difference between H7/g6 and H7/p6?
H7/g6 is a clearance (sliding) fit - the shaft is always smaller than the hole, so parts slide or rotate freely, used for guide bushes and spigots. H7/p6 is an interference (press) fit - the shaft is larger than the hole, so the parts must be pressed together for a permanent joint, used for bushes in housings.
What does the number in a fit like H7 mean?
The number is the IT (International Tolerance) grade, which sets the width of the tolerance band. A smaller number is a tighter, more precise tolerance. IT6 and IT7 are typical for machined shafts and holes; IT11 is a coarse grade for rough fits. The band width also grows with the part diameter.