ISO 286 fit calculator & ISO 2768 tolerance reference
Use this free reference to compare hole and shaft limits, understand fit clearance, and distinguish a feature tolerance from an assembly tolerance stack. The calculator covers a selected ISO 286 subset; it does not replace the complete standard or your drawing requirements.
ISO 286 — Ø12 mm
| Fit | Hole (mm) | Shaft (mm) | Clearance (mm) |
|---|---|---|---|
| H7/g6 | 0 / +0.018 | -0.017 / -0.006 | +0.006 … +0.035 |
| H8/f7 | 0 / +0.027 | -0.034 / -0.016 | +0.016 … +0.061 |
| H7/h6 | 0 / +0.018 | -0.011 / 0 | 0 … +0.029 |
| H7/k6 | 0 / +0.018 | +0.001 / +0.012 | -0.012 … +0.017 |
| H7/p6 | 0 / +0.018 | +0.018 / +0.029 | -0.029 … 0 |
ISO 2768-1 — linear dimensions (mm)
| Nominal (mm) | f | m | c |
|---|---|---|---|
| 0.5 – 3 | ±0.05 | ±0.10 | ±0.20 |
| 3 – 6 | ±0.05 | ±0.10 | ±0.30 |
| 6 – 30 | ±0.10 | ±0.20 | ±0.50 |
| 30 – 120 | ±0.15 | ±0.30 | ±0.80 |
| 120 – 400 | ±0.20 | ±0.50 | ±1.20 |
What do H7/g6 and H8/f7 mean?
In ISO fit notation, the letter identifies the tolerance-zone position and the number identifies the IT grade. Uppercase letters refer to holes and lowercase letters to shafts. In a hole-basis H fit, the hole’s lower deviation is zero. H7/g6 and H8/f7 are clearance-fit examples; their actual deviations depend on the nominal size band. A fit controls size relationships, not the location or orientation of the features.
How is clearance calculated?
Minimum clearance is the smallest permitted hole minus the largest permitted shaft. Maximum clearance is the largest permitted hole minus the smallest permitted shaft. Positive clearance indicates a gap; negative clearance indicates interference. If the permitted interval spans negative and positive values, the pair is a transition fit. All displayed limits and clearances are in millimetres.
When does ISO 2768 general tolerance apply?
ISO 2768-1 addresses linear and angular dimensions without individual tolerance indications when the drawing invokes that standard. The general-tolerance tab shows a selected linear-dimension reference for classes f, m and c. A dimension already marked 15 ±0.1 keeps that explicit tolerance; a general-tolerance class must not replace it.
Why can an acceptable fit still fail an assembly requirement?
A fit lookup checks one mating size relationship. An assembly key characteristic may also depend on hole positions, link lengths, datums, several joints and sensitivity to motion. A tolerance stack must follow the actual datum-to-feature path. Sliding travel is a motion range, and should be identified separately from manufacturing variation.
Common questions
Is this fit calculator free?
Yes. The Standards reference and fit calculator are public and require neither a sign-in nor a subscription. Analyzing an uploaded NX part is a separate workspace service.
Which sizes and fits does the calculator support?
Nominal diameters greater than zero and up to 500 mm; hole-basis H; IT5–IT8 for both members; and shaft zones f, g, h, k and p. Other combinations are rejected rather than extrapolated.
Does H7/g6 specify a positional tolerance?
No. H7/g6 specifies the size tolerance zones of a hole and shaft. Position, orientation and form controls must be considered separately where the function requires them.
What is the difference between worst-case and RSS stack-up?
Worst-case sums the absolute contributions after applying their sensitivities. Root-sum-square (RSS) combines independent contributions quadratically under stated statistical assumptions. RSS is not a guarantee that every possible assembly meets the limits.
What happens when a key characteristic is out of tolerance?
SuperNX reports the failing characteristic and its contributors. PMI write-back is gated: a run with a failing key characteristic does not produce a toleranced part copy.