ISO metric · coarse
M4 × 0.7 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
3.4 mm
0.1339" · 66% thread
Form tap
3.7 mm
0.1457" · 63% thread
Pick your material for its % of thread, tapping RPM and the rigid-tap code.
Thread dimensions
- Major Ø
- 4.000 mm (0.1575")
- Pitch
- 0.7 mm
- Pitch Ø (basic)
- 3.545 mm (0.1396")
- Minor Ø (internal, basic)
- 3.242 mm (0.1276")
- Thread depth (internal)
- 0.379 mm (0.0149")
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 |
|---|---|---|---|
| #30 | 0.1285 | 3.26 | 81% |
| 3.3 mm | 0.1299 | 3.30 | 77% |
| 3.4 mmsuggested | 0.1339 | 3.40 | 66% |
| #29 | 0.1360 | 3.45 | 60% |
| 3.5 mm | 0.1378 | 3.50 | 55% |
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 |
|---|---|---|---|
| 3.6 mm | 0.1417 | 3.60 | 84% |
| #27 | 0.1440 | 3.66 | 72% |
| 3.7 mm | 0.1457 | 3.70 | 63% |
| #26 | 0.1470 | 3.73 | 56% |
3-wire measurement
- Best wire size
- 0.404 mm (0.0159")
- Over wires, at basic pitch Ø
- 4.152 mm (0.1634")
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