1-1/2-8 tap drill size
Use a 1-3/8 drill (1.3750 in) for a 1-1/2-8 cutting tap at 75% thread.
| Tap type | Drill | Decimal (in) |
|---|---|---|
| Cutting tap, 75% thread | 1-3/8 | 1.3750 |
| Cutting tap, 50% thread (hard material) | 1-27/64 | 1.4219 |
| Roll / form tap, 65% thread | 1-7/16 | 1.4375 |
- Pitch
- 3.175 mm (8 TPI)
- Major Ø
- 1.5000
- Pitch Ø
- 1.4188
- Minor Ø
- 1.3647
Common questions
- What size drill for a 1-1/2-8 tap?
- Use a 1-3/8 drill (1.3750 in) for a 1-1/2-8 cutting tap at 75% thread.
- What drill for a 1-1/2-8 roll (form) tap?
- About 1.4448 in; the nearest standard drill is 1-7/16. Check your tap maker's table.
Other 8UN sizes
Drill sizes from Machinery's Handbook and ASME B1.1/B1.13M; roll tap sizes from the form-tap formula. Tap and insert makers' tables are authoritative.
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