CNC Machinist Calculator UltraHome › Guides
ISO fit tolerances
An ISO 286 fit such as H7/g6 names a tolerance zone for the hole (capital letter) and one for the shaft (lower case). The letter sets where the zone sits; the number sets how wide it is.
Hole-basis fits
Most shops use the hole-basis system: the hole is H (its lower limit is exactly the nominal size) and the shaft letter picks the fit.
- Clearance (always a gap): H7/g6 for precise sliding, H7/h6 for locating parts that must assemble by hand.
- Transition (gap or slight press): H7/k6 for accurate location, such as gears and couplings.
- Interference (always a press): H7/p6 for a light press fit, H7/s6 for a medium drive fit.
Worked example: 25 mm bore
For sizes over 18 up to 30 mm, IT7 is 21 µm and IT6 is 13 µm.
| Fit | Hole (H7) | Shaft | Result |
|---|---|---|---|
| H7/g6 | 25.000 / 25.021 | 24.980 / 24.993 (g6) | Clearance 0.007 to 0.041 mm |
| H7/k6 | 25.000 / 25.021 | 25.002 / 25.015 (k6) | Clearance up to 0.019, interference up to 0.015 mm |
| H7/p6 | 25.000 / 25.021 | 25.022 / 25.035 (p6) | Interference 0.001 to 0.035 mm |
Maximum clearance = largest hole − smallest shaft. Maximum interference = largest shaft − smallest hole.
Any size, any fit, inch or metric. Enter a nominal size and the hole and shaft zones, and the app gives both limits and the resulting clearance or interference.
Open the fit tolerance calculator