1/2-13 tap drill size
Use a 27/64" drill (0.4219 in) for a 1/2-13 cutting tap at 75% thread.
| Tap type | Drill | Decimal (in) |
|---|---|---|
| Cutting tap, 75% thread | 27/64" | 0.4219 |
| Cutting tap, 50% thread (hard material) | 29/64" | 0.4531 |
| Roll / form tap, 65% thread | 15/32 | 0.4688 |
| Helicoil / STI insert (1/2-13×1D) | 33/64" | 0.5156 |
- Pitch
- 1.9538 mm (13 TPI)
- Major Ø
- 0.5000
- Pitch Ø
- 0.4500
- Minor Ø
- 0.4056
1/2-13 tapping speeds and feeds
Feed = pitch (0.0769 in per rev). Starting points for a general-purpose HSS cut tap:
- Aluminum 6061 / 7075: 530 RPM · 40.8 IPM
- Free-machining / mild steel: 150 RPM · 11.5 IPM
- 304 / 316 stainless: 80 RPM · 6.15 IPM
1/2-13 tap speeds and feeds: all materials, form taps and G84 code · 27/64" drill size and speeds
Common questions
- What size drill for a 1/2-13 tap?
- Use a 27/64" drill (0.4219 in) for a 1/2-13 cutting tap at 75% thread.
- What drill for a 1/2-13 roll (form) tap?
- About 0.4660 in; the nearest standard drill is 15/32. Check your tap maker's table.
- What drill for a 1/2-13 Helicoil?
- Drill 33/64" (0.5156 in), then tap with the 1/2-13 STI tap.
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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