ISO 286 Fit Tolerance Chart: H7/p6, H7/h6, H7/g6 and More

Published 28 September 2026. Last checked 28 September 2026 by The CheckedCalc editor.

A fit tolerance chart tells you how loose or how tight a hole and a shaft of the same nominal size can be once both parts are anywhere inside their tolerances. This page gives the answer for the ten preferred hole-basis fits, from the loose running H11/c11 to the force fit H7/u6, for every ISO 286 size range up to 500 mm. Every limit in the tables is computed from the ISO 286-1:2010 standard tolerance grades and fundamental deviations. The same code runs the press fit calculator and is tested against published ISO 286-2 limit tables. Nothing is typed in by hand.

How to read a fit such as 25 H7/p6

The number is the nominal size in millimetres, shared by both parts. The capital letter and number give the hole tolerance class, the lower-case pair the shaft. The letter fixes where the tolerance zone sits relative to the nominal size (the fundamental deviation); the number is the standard tolerance grade, IT7 or IT6 here, which fixes how wide the zone is. ISO 286-1 tables both as deviations in micrometres: ES and EI for the upper and lower deviation of the hole, es and ei for the shaft.

In the hole-basis system every hole is an H, whose lower deviation is zero, so the hole never goes below nominal size. The shaft letter alone then sets the character of the fit. Letters before h give clearance, and h gives a zero-clearance limit. Letters from k onwards move the shaft zone above the hole zone, into transition and then interference. ISO 286-1 recommends the hole-basis system for general use because it keeps the number of reamers, broaches and plug gauges in the workshop down. Grinding a shaft to an unusual deviation is cheaper than making a hole to one.

Worked through for 25 H7/p6: the H7 hole is +21 / 0 µm, so 25.000 to 25.021 mm. The p6 shaft is +35 / +22 µm, so 25.022 to 25.035 mm. The loosest pair is the largest hole on the smallest shaft, ES − ei = −1 µm, which is 1 I. The tightest pair is the smallest hole on the largest shaft, EI − es = −35 µm, which is 35 I. In the tables, C marks clearance and I marks interference.

Which fit to use

The ten fits below are the preferred hole-basis fits of ASME B4.2, which uses the ISO tolerance classes unchanged. All of them sit inside the wider selection of preferable fits in ISO 286-1:2010 Figure 12. The descriptions are paraphrased from ASME B4.2. Pick the loosest fit that does the job: every step tighter costs assembly force, stress in the hub and inspection effort.

H7/h6 is a clearance fit on paper, but its tightest case is exactly zero clearance (0 at 25 mm), so some pairs will need a light push. It is a location fit, not a running fit. A transition fit such as H7/k6 or H7/n6 can come out either way on any given pair. Use it where location matters more than whether a particular part slides or needs a press, and never rely on it to transmit torque.

Fit type also depends on size. Over 3 mm the loosest H7/p6 pair never has clearance (at some small sizes it is exactly line to line). Up to 3 mm it can have 4 µm of clearance, so there it behaves as a transition fit, as ASME B4.2 also notes.

For interference fits the chart gives the geometry only. Whether H7/s6 on a steel shaft in an aluminium hub will transmit your torque, or yield the hub, depends on the contact pressure from the Lamé thick-cylinder equations, the friction coefficient and the temperature. Run the pair through the press fit calculator, which takes the same ISO codes and returns pressure, holding torque, assembly force, hub stress and the shrink-fit temperature.

What the chart does not cover

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