ISO metric · coarse
M1.2 × 0.25 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
1 mm
0.0394" · 62% thread
Form tap
1.1 mm
0.0433" · 59% thread
Pick your material for its % of thread, tapping RPM and the rigid-tap code.
Thread dimensions
- Major Ø
- 1.200 mm (0.0472")
- Pitch
- 0.25 mm
- Pitch Ø (basic)
- 1.038 mm (0.0409")
- Minor Ø (internal, basic)
- 0.929 mm (0.0366")
- Thread depth (internal)
- 0.135 mm (0.0053")
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 |
|---|---|---|---|
| #63 | 0.0370 | 0.94 | 80% |
| #62 | 0.0380 | 0.97 | 72% |
| #61 | 0.0390 | 0.99 | 64% |
| 1 mm | 0.0394 | 1.00 | 62% |
| #60 | 0.0400 | 1.02 | 57% |
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 |
|---|---|---|---|
| #58 | 0.0420 | 1.07 | 78% |
| #57 | 0.0430 | 1.09 | 63% |
| 1.1 mm | 0.0433 | 1.10 | 59% |
3-wire measurement
- Best wire size
- 0.144 mm (0.0057")
- Over wires, at basic pitch Ø
- 1.254 mm (0.0494")
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