7/8-14 tap drill size
Use a 13/16 drill (0.8125 in) for a 7/8-14 cutting tap at 75% thread.
| Tap type | Drill | Decimal (in) |
|---|---|---|
| Cutting tap, 75% thread | 13/16 | 0.8125 |
| Cutting tap, 50% thread (hard material) | 53/64 | 0.8281 |
| Roll / form tap, 65% thread | 27/32 | 0.8438 |
- Pitch
- 1.8143 mm (14 TPI)
- Major Ø
- 0.8750
- Pitch Ø
- 0.8286
- Minor Ø
- 0.7977
7/8-14 tapping speeds and feeds
Feed = pitch (0.0714 in per rev). Starting points for a general-purpose HSS cut tap:
- Aluminum 6061 / 7075: 310 RPM · 22.1 IPM
- Free-machining / mild steel: 90 RPM · 6.43 IPM
- 304 / 316 stainless: 40 RPM · 2.86 IPM
7/8-14 tap speeds and feeds: all materials, form taps and G84 code · 13/16 drill size and speeds
Common questions
- What size drill for a 7/8-14 tap?
- Use a 13/16 drill (0.8125 in) for a 7/8-14 cutting tap at 75% thread.
- What drill for a 7/8-14 roll (form) tap?
- About 0.8434 in; the nearest standard drill is 27/32. Check your tap maker's table.
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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