H8 table
| Diameter (mm) | Upper (µm) | Lower (µm) | Example: limit sizes |
|---|---|---|---|
| ≤ 3 | +14 | 0 | Ø3: 3.000 – 3.014 |
| 3–6 | +18 | 0 | Ø6: 6.000 – 6.018 |
| 6–10 | +22 | 0 | Ø10: 10.000 – 10.022 |
| 10–18 | +27 | 0 | Ø18: 18.000 – 18.027 |
| 18–30 | +33 | 0 | Ø30: 30.000 – 30.033 |
| 30–50 | +39 | 0 | Ø50: 50.000 – 50.039 |
| 50–80 | +46 | 0 | Ø80: 80.000 – 80.046 |
| 80–120 | +54 | 0 | Ø120: 120.000 – 120.054 |
| 120–180 | +63 | 0 | Ø180: 180.000 – 180.063 |
| 180–250 | +72 | 0 | Ø250: 250.000 – 250.072 |
| 250–315 | +81 | 0 | Ø315: 315.000 – 315.081 |
| 315–400 | +89 | 0 | Ø400: 400.000 – 400.089 |
| 400–500 | +97 | 0 | Ø500: 500.000 – 500.097 |
How to read it
The letter tells where the tolerance zone sits relative to the nominal size, the number how wide it is (grade IT8). Capitals are for holes, lower case for shafts. With H the lower limit is always zero: the hole is never smaller than nominal. It is the basis of the hole-basis system, the most used in workshops.
Fits using H8
Other classes
Values computed from the IT grades and fundamental deviations of ISO 286-1, checked against several published tables. For critical designs the standard itself is what counts.