ISO metric · coarse
M2 × 0.4 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
1.6 mm
0.0630" · 77% thread
Form tap
1.8 mm
0.0709" · 74% thread
Pick your material for its % of thread, tapping RPM and the rigid-tap code.
Thread dimensions
- Major Ø
- 2.000 mm (0.0787")
- Pitch
- 0.4 mm
- Pitch Ø (basic)
- 1.740 mm (0.0685")
- Minor Ø (internal, basic)
- 1.567 mm (0.0617")
- Thread depth (internal)
- 0.217 mm (0.0085")
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 |
|---|---|---|---|
| 1/16 | 0.0625 | 1.59 | 79% |
| 1.6 mm | 0.0630 | 1.60 | 77% |
| #52 | 0.0635 | 1.61 | 74% |
| 1.7 mm | 0.0669 | 1.70 | 58% |
| #51 | 0.0670 | 1.70 | 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 |
|---|---|---|---|
| #50 | 0.0700 | 1.78 | 82% |
| 1.8 mm | 0.0709 | 1.80 | 74% |
| #49 | 0.0730 | 1.85 | 54% |
3-wire measurement
- Best wire size
- 0.231 mm (0.0091")
- Over wires, at basic pitch Ø
- 2.087 mm (0.0821")
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