GO / NO-GO gauge tolerances
A 30 H9 hole (30.000 to 30.052 mm) takes a GO plug of 30.009 ± 0.002 mm, worn out at 30.000 mm, and a NO-GO plug of 30.052 ± 0.002 mm. Choose a hole or a shaft and enter its size and class for the GO and NO-GO gauge sizes, the gauge maker’s tolerance on each, and how far the GO gauge may wear, with the gauges’ zones drawn to scale against the part’s.
- GO gauge, new
- NO-GO gauge
- GO worn out at
- Part limits, H9
- 30.000 to 30.052mm
- Gauge values
- Z 9 · H/2 2 · Y 0µm
- NO-GO form
- Full cylinder, ± H/2
How it’s calculated
With K the hole’s lower limit and G its upper: GO new = K + Z ± H/2; GO worn out at K − Y + α; NO-GO = G − α ± H/2. A spherical gauge takes Hs/2: the NO-GO over 6 mm, the GO only over 180 mm. α is 0 up to 180 mm. Y is 0 from grade 9: the gauge wears out at the limit. The part’s limits are ISO 286-2:2010’s.
Gauge values, over 18 to 30 mm µm
| Grade | T | H/2 | Hs/2 | Y | Z | α |
|---|---|---|---|---|---|---|
| 6 | 13 | 1.25 | 1.25 | 1.5 | 2 | 0 |
| 7 | 21 | 2 | 1.25 | 3 | 3 | 0 |
| 8 | 33 | 2 | 1.25 | 4 | 5 | 0 |
| 9 | 52 | 2 | 1.25 | 0 | 9 | 0 |
| 10 | 84 | 2 | 1.25 | 0 | 9 | 0 |
| 11 | 130 | 4.5 | 3 | 0 | 19 | 0 |
| 12 | 210 | 4.5 | 3 | 0 | 19 | 0 |
| 13 | 330 | 10.5 | 6.5 | 0 | 36 | 0 |
| 14 | 520 | 10.5 | 6.5 | 0 | 36 | 0 |
| 15 | 840 | 10.5 | 6.5 | 0 | 72 | 0 |
| 16 | 1300 | 10.5 | 6.5 | 0 | 72 | 0 |
Why is a new GO gauge not made to the limit?
The GO gauge is the one that wears: it enters every good part. So a new one is made a little inside the part’s tolerance, by Z, and used until it has worn to the wear limit, which for the finer grades is just past the part’s limit, by Y. The NO-GO gauge should never enter a good part, so it barely wears and is made on the limit itself. Over 180 mm a gauge cannot be measured as closely, so both move inside the part’s tolerance by a safety zone, α: measurement doubt then rejects a good part rather than passing a bad one.