M20×2.5 tap drill size
Use a 17.5mm drill (17.50 mm) for a M20×2.5 cutting tap at 75% thread.
| Tap type | Drill | Decimal (mm) |
|---|---|---|
| Cutting tap, 75% thread | 17.5mm | 17.50 |
| Cutting tap, 50% thread (hard material) | 18.0mm | 18.00 |
| Roll / form tap, 65% thread | 18.90 mm | 18.90 |
| Helicoil / STI insert (M20×2.5×1D) | 21.5mm | 21.50 |
- Pitch
- 2.5 mm
- Major Ø
- 20.00
- Pitch Ø
- 18.38
- Minor Ø
- 17.29
Common questions
- What size drill for a M20×2.5 tap?
- Use a 17.5mm drill (17.50 mm) for a M20×2.5 cutting tap at 75% thread.
- What drill for a M20×2.5 roll (form) tap?
- About 18.89 mm; the nearest standard drill is 18.90 mm. Check your tap maker's table.
- What drill for a M20×2.5 Helicoil?
- Drill 21.5mm (21.50 mm), then tap with the M20×2.5 STI tap.
Other Metric 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.