ISO metric · coarse
M3.5 × 0.6 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 mm
0.1181" · 64% thread
Form tap
3.2 mm
0.1260" · 74% thread
Pick your material for its % of thread, tapping RPM and the rigid-tap code.
Thread dimensions
- Major Ø
- 3.500 mm (0.1378")
- Pitch
- 0.6 mm
- Pitch Ø (basic)
- 3.110 mm (0.1225")
- Minor Ø (internal, basic)
- 2.850 mm (0.1122")
- Thread depth (internal)
- 0.325 mm (0.0128")
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 |
|---|---|---|---|
| #33 | 0.1130 | 2.87 | 81% |
| 2.9 mm | 0.1142 | 2.90 | 77% |
| #32 | 0.1160 | 2.95 | 71% |
| 3 mm | 0.1181 | 3.00 | 64% |
| #31 | 0.1200 | 3.05 | 58% |
| 3.1 mm | 0.1220 | 3.10 | 51% |
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 |
|---|---|---|---|
| 1/8 | 0.1250 | 3.18 | 80% |
| 3.2 mm | 0.1260 | 3.20 | 74% |
| #30 | 0.1285 | 3.26 | 58% |
3-wire measurement
- Best wire size
- 0.346 mm (0.0136")
- Over wires, at basic pitch Ø
- 3.630 mm (0.1429")
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