ISO metric · coarse
M1.6 × 0.35 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
1.3 mm
0.0512" · 66% thread
Form tap
1.4 mm
0.0551" · 84% thread
Pick your material for its % of thread, tapping RPM and the rigid-tap code.
Thread dimensions
- Major Ø
- 1.600 mm (0.0630")
- Pitch
- 0.35 mm
- Pitch Ø (basic)
- 1.373 mm (0.0540")
- Minor Ø (internal, basic)
- 1.221 mm (0.0481")
- Thread depth (internal)
- 0.189 mm (0.0075")
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 |
|---|---|---|---|
| 1.3 mmsuggested | 0.0512 | 1.30 | 66% |
| #55 | 0.0520 | 1.32 | 61% |
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 |
|---|---|---|---|
| 1.4 mm | 0.0551 | 1.40 | 84% |
3-wire measurement
- Best wire size
- 0.202 mm (0.0080")
- Over wires, at basic pitch Ø
- 1.676 mm (0.0660")
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