ISO 286 fits: H7/g6, H7/h6, H7/p6 chart and clearance calculator
Published September 28, 2026 — deviations, min/max sizes and clearance or interference for any diameter up to 500 mm, the deviation chart of the most used classes, and a method to choose a fit without over-specifying.
ISO 286 fit calculator
Enter the nominal diameter and both tolerance classes: you get the ISO 286 deviations, the min/max sizes and the clearance or interference of the fit. Deviations are in micrometres (µm), sizes in millimetres.
How to read it: a negative clearance is an interference. If the minimum clearance is positive, the fit is a clearance fit; if the maximum clearance is negative, it's an interference fit; in between, it's a transition fit: depending on the actual parts, you get slight play or slight interference.
1. The 8 fits to know, and when to use them
The hole-basis system (H hole, you choose the shaft) is by far the most used: one reamer or hole tolerance across the range, and the shaft, easier to machine precisely, carries the function. These eight pairs cover almost all general engineering.
For rolling bearings, don't pick from this table: the shaft and housing tolerance depends on the load (rotating or stationary) and its magnitude. Bearing manufacturers publish their own recommendations — they take precedence.
2. Deviation chart: H7 and the most common shafts
Upper / lower deviations in micrometres, by nominal size range (over … up to and including …). Example: a Ø 25 g6 shaft measures between 24.980 and 24.993 mm.
Values from the ISO 286-2 tables: IT tolerance grades and fundamental deviations from ISO 286-1. The calculator above uses the same data, including the Δ correction for K, M, N and P holes.
3. Reading “Ø 25 H7/g6”: the letter and the number
- The letter positions the tolerance zone relative to the nominal size. Upper case for holes, lower case for shafts. H and h touch the nominal size (zero deviation); a to g lie below it for a shaft (clearance), k to zc above it (interference).
- The number is the IT grade: the width of the zone. The smaller it is, the more precise and expensive. IT6–IT7: precision machining (grinding, reaming); IT8–IT9: careful turning and milling; IT11: ordinary machining, rough parts.
- The hole takes one grade more than the shaft (H7 with g6, H8 with f7): a precise hole is harder to make than a precise shaft.
On a drawing, put the tolerance on each part (Ø 25 H7 on the hub, Ø 25 g6 on the shaft): the H7/g6 notation only makes sense on an assembly drawing. In SOLIDWORKS, the dimension accepts the fit directly (dimension properties → Tolerance/Precision → Fit), which avoids hand-typed deviations — one of the most common SOLIDWORKS mistakes on drawings. For the fit to guarantee assembly even with a form error, add the envelope requirement Ⓔ (see geometrical tolerancing modifiers).
4. Choosing without over-specifying: three questions
- Must the part move? Yes → clearance fit (f, g, h). No, and it transmits load → interference (p, s). No, but it must come apart → transition (k, n) with an anti-rotation feature (key, splines).
- What position accuracy? 40 µm of play on a location is amplified at the end of a lever arm. If the function tolerates 0.1 mm, a much cheaper H9/d9 is enough.
- Who makes it, and how? IT6 requires grinding. If the shop or supplier doesn't grind, an H7/g6 on the drawing will either be out of tolerance or billed accordingly.
For every dimension without a stated tolerance, the title-block general tolerance applies: see ISO 2768 general tolerances. And a tight tolerance without a suitable surface finish can't be measured: the Ra roughness chart gives the values consistent with each grade.
5. FAQ
What does H7/g6 mean?
It's a close sliding fit in the hole-basis system: the hole is H7 (zero lower deviation, grade 7), the shaft g6 (slightly below nominal, grade 6). For Ø 25 mm: hole 25.000 to 25.021, shaft 24.980 to 24.993, giving 7 to 41 µm of clearance.
What is the H7 tolerance for a 20 mm diameter?
+21 / 0 µm: Ø 20 H7 measures between 20.000 and 20.021 mm. Ø 20 falls in the over 18 up to 30 mm range, whose IT7 grade is 21 µm.
Which fit for a dowel pin?
Hardened parallel pins (ISO 8734) are m6: tight in an H7 hole in the part that holds them, with an H7 or slightly looser hole in the part that locates on them, so it can be removed.
What is the difference between h6 and g6?
Same tolerance width (grade 6), but g6 sits below the nominal size. With an H7 hole, h6 gives zero minimum clearance (location), g6 a small guaranteed clearance (a few µm) that allows sliding.
Why does the hole take one grade more than the shaft?
Because a precise hole is harder to machine and inspect than a precise shaft. Giving the hole one more grade (H7 vs 6 for the shaft) balances the cost between both parts for an equivalent functional clearance.