7/16-20 tap drill size
Use a 25/64" drill (0.3906 in) for a 7/16-20 cutting tap at 75% thread.
| Tap type | Drill | Decimal (in) |
|---|---|---|
| Cutting tap, 75% thread | 25/64" | 0.3906 |
| Cutting tap, 50% thread (hard material) | Y | 0.4040 |
| Roll / form tap, 65% thread | Z | 0.4130 |
| Helicoil / STI insert (7/16-20×1D) | 31/64" | 0.4844 |
- Pitch
- 1.27 mm (20 TPI)
- Major Ø
- 0.4375
- Pitch Ø
- 0.4050
- Minor Ø
- 0.3762
7/16-20 tapping speeds and feeds
Feed = pitch (0.0500 in per rev). Starting points for a general-purpose HSS cut tap:
- Aluminum 6061 / 7075: 610 RPM · 30.5 IPM
- Free-machining / mild steel: 170 RPM · 8.50 IPM
- 304 / 316 stainless: 90 RPM · 4.50 IPM
7/16-20 tap speeds and feeds: all materials, form taps and G84 code · 25/64" drill size and speeds
Common questions
- What size drill for a 7/16-20 tap?
- Use a 25/64" drill (0.3906 in) for a 7/16-20 cutting tap at 75% thread.
- What drill for a 7/16-20 roll (form) tap?
- About 0.4154 in; the nearest standard drill is Z. Check your tap maker's table.
- What drill for a 7/16-20 Helicoil?
- Drill 31/64" (0.4844 in), then tap with the 7/16-20 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.
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