1-1/4-18 tap drill size
Use a 1-13/64 drill (1.2031 in) for a 1-1/4-18 cutting tap at 75% thread.
| Tap type | Drill | Decimal (in) |
|---|---|---|
| Cutting tap, 75% thread | 1-13/64 | 1.2031 |
| Cutting tap, 50% thread (hard material) | 1-7/32 | 1.2188 |
| Roll / form tap, 65% thread | 1-7/32 | 1.2188 |
- Pitch
- 1.4111 mm (18 TPI)
- Major Ø
- 1.2500
- Pitch Ø
- 1.2139
- Minor Ø
- 1.1899
Common questions
- What size drill for a 1-1/4-18 tap?
- Use a 1-13/64 drill (1.2031 in) for a 1-1/4-18 cutting tap at 75% thread.
- What drill for a 1-1/4-18 roll (form) tap?
- About 1.2254 in; the nearest standard drill is 1-7/32. Check your tap maker's table.
Other UNEF 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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