9/16-18 tap drill size
Use a 33/64" drill (0.5156 in) for a 9/16-18 cutting tap at 75% thread.
| Tap type | Drill | Decimal (in) |
|---|---|---|
| Cutting tap, 75% thread | 33/64" | 0.5156 |
| Cutting tap, 50% thread (hard material) | 17/32" | 0.5312 |
| Roll / form tap, 65% thread | 17/32 | 0.5313 |
| Helicoil / STI insert (9/16-18×1D) | 39/64" | 0.6094 |
- Pitch
- 1.4111 mm (18 TPI)
- Major Ø
- 0.5625
- Pitch Ø
- 0.5264
- Minor Ø
- 0.4943
Common questions
- What size drill for a 9/16-18 tap?
- Use a 33/64" drill (0.5156 in) for a 9/16-18 cutting tap at 75% thread.
- What drill for a 9/16-18 roll (form) tap?
- About 0.5379 in; the nearest standard drill is 17/32. Check your tap maker's table.
- What drill for a 9/16-18 Helicoil?
- Drill 39/64" (0.6094 in), then tap with the 9/16-18 STI tap.
Other UNF 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.