ISO metric · coarse
M16 × 2 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
14 mm
0.5512" · 77% thread
Or 9/16 (0.5625") for 66%
Form tap
15 mm
0.5906" · 74% thread
Or 19/32 (0.5938") for 68%
Pick your material for its % of thread, tapping RPM and the rigid-tap code.
Thread dimensions
- Major Ø
- 16.000 mm (0.6299")
- Pitch
- 2 mm
- Pitch Ø (basic)
- 14.701 mm (0.5788")
- Minor Ø (internal, basic)
- 13.835 mm (0.5447")
- Thread depth (internal)
- 1.083 mm (0.0426")
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 |
|---|---|---|---|
| 35/64 | 0.5469 | 13.89 | 81% |
| 14 mm | 0.5512 | 14.00 | 77% |
| 9/16suggested | 0.5625 | 14.29 | 66% |
| 14.5 mm | 0.5709 | 14.50 | 58% |
| 37/64 | 0.5781 | 14.68 | 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 |
|---|---|---|---|
| 15 mm | 0.5906 | 15.00 | 74% |
| 19/32suggested | 0.5938 | 15.08 | 68% |
3-wire measurement
- Best wire size
- 1.155 mm (0.0455")
- Over wires, at basic pitch Ø
- 16.433 mm (0.6470")
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