ISO metric · coarse
M12 × 1.75 tap drill size
For general work, OSG suggests 65–70% of full thread. Harder materials and deep holes want less; the calculator sets it from your material.
Cut tap
10.5 mm
0.4134" · 66% thread
Form tap
11.2 mm
0.4409" · 67% thread
Pick your material for its % of thread, tapping RPM and the rigid-tap code.
Thread dimensions
- Major Ø
- 12.000 mm (0.4724")
- Pitch
- 1.75 mm
- Pitch Ø (basic)
- 10.863 mm (0.4277")
- Minor Ø (internal, basic)
- 10.106 mm (0.3979")
- Thread depth (internal)
- 0.947 mm (0.0373")
Basic sizes of the 60° form. Tolerance classes (6H) set the limits around them.
Cut tap drills
For a cutting (fluted or spiral) tap. Every standard drill from 50% to 85% thread; suggested rows are in the 65–70% band.
| Drill | Ø in | Ø mm | Thread |
|---|---|---|---|
| X | 0.3970 | 10.08 | 84% |
| 10.1 mm | 0.3976 | 10.10 | 84% |
| 10.2 mm | 0.4016 | 10.20 | 79% |
| Y | 0.4040 | 10.26 | 76% |
| 10.3 mm | 0.4055 | 10.30 | 75% |
| 13/32 | 0.4063 | 10.32 | 74% |
| 10.4 mmsuggested | 0.4094 | 10.40 | 70% |
| Zsuggested | 0.4130 | 10.49 | 66% |
| 10.5 mmsuggested | 0.4134 | 10.50 | 66% |
| 10.6 mm | 0.4173 | 10.60 | 62% |
| 10.7 mm | 0.4213 | 10.70 | 57% |
| 27/64 | 0.4219 | 10.72 | 56% |
| 10.8 mm | 0.4252 | 10.80 | 53% |
Form tap drills
A form (roll) tap displaces metal instead of cutting it, so it needs a bigger hole. Every standard drill from 50% to 85% thread; suggested rows are in the 65–70% band.
| Drill | Ø in | Ø mm | Thread |
|---|---|---|---|
| 11 mm | 0.4331 | 11.00 | 84% |
| 11.1 mm | 0.4370 | 11.10 | 76% |
| 7/16 | 0.4375 | 11.11 | 75% |
| 11.2 mmsuggested | 0.4409 | 11.20 | 67% |
| 11.3 mm | 0.4449 | 11.30 | 59% |
| 11.4 mm | 0.4488 | 11.40 | 50% |
3-wire measurement
- Best wire size
- 1.010 mm (0.0398")
- Over wires, at basic pitch Ø
- 12.379 mm (0.4874")
For the external thread (the screw). The best wire touches the flanks at the pitch diameter.
Sources
- ISO 261 / ISO 262 — ISO general purpose metric screw threads: general plan and selected sizes
- OSG — Tap drill size and pitch diameter limit chart (formula, suggested % of full thread)
- Cutting Tool Engineering — "Threads will roll": form tap hole size = D − 0.0068 × % / TPI
- ASME B94.11M — Twist drills (fractional, number, letter and metric sizes)
- NIST (NBS) Letter Circular 23 and Pratt & Whitney — three-wire thread measurement, best wire size