3-1/4-4 tap drill size
Use a 3 drill (3.0000 in) for a 3-1/4-4 cutting tap at 75% thread.
| Tap type | Drill | Decimal (in) |
|---|---|---|
| Cutting tap, 75% thread | 3 | 3.0000 |
| Cutting tap, 50% thread (hard material) | 3-1/16 | 3.0625 |
| Roll / form tap, 65% thread | 3-1/8 | 3.1250 |
- Pitch
- 6.35 mm (4 TPI)
- Major Ø
- 3.2500
- Pitch Ø
- 3.0876
- Minor Ø
- 2.9794
Common questions
- What size drill for a 3-1/4-4 tap?
- Use a 3 drill (3.0000 in) for a 3-1/4-4 cutting tap at 75% thread.
- What drill for a 3-1/4-4 roll (form) tap?
- About 3.1395 in; the nearest standard drill is 3-1/8. Check your tap maker's table.
Other UNC 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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