UNC (Unified Coarse)
| Nominal | Major dia (in) | TPI | Tap drill |
|---|---|---|---|
| #4 | 0.112 | 40 | #43 (0.089") |
| #6 | 0.138 | 32 | #36 (0.106") |
| #8 | 0.164 | 32 | #29 (0.136") |
| #10 | 0.190 | 24 | #25 (0.150") |
| 1/4 | 0.250 | 20 | #7 (0.201") |
| 5/16 | 0.3125 | 18 | F (0.257") |
| 3/8 | 0.375 | 16 | 5/16" (0.3125") |
| 7/16 | 0.4375 | 14 | U (0.368") |
| 1/2 | 0.500 | 13 | 27/64" (0.422") |
| 5/8 | 0.625 | 11 | 17/32" (0.531") |
| 3/4 | 0.750 | 10 | 21/32" (0.656") |
| 1 | 1.000 | 8 | 7/8" (0.875") |
ISO metric coarse
| Size | Pitch (mm) | Tap drill (mm) |
|---|---|---|
| M2 | 0.4 | 1.6 |
| M2.5 | 0.45 | 2.05 |
| M3 | 0.5 | 2.5 |
| M4 | 0.7 | 3.3 |
| M5 | 0.8 | 4.2 |
| M6 | 1.0 | 5.0 |
| M8 | 1.25 | 6.8 |
| M10 | 1.5 | 8.5 |
| M12 | 1.75 | 10.2 |
| M16 | 2.0 | 14.0 |
| M20 | 2.5 | 17.5 |
| M24 | 3.0 | 21.0 |
Notes
- Tap drill sizes give ~75% thread engagement — standard for hand tapping.
- UNF (fine) has more threads per inch than UNC — stronger, less prone to vibration loosening.
- Metric fine exists (e.g. M8 × 1.0) for the same reason.
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