ISO metric · fine
M45 × 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
41.5 mm
1.6339" · 67% thread
Form tap
43 mm
1.6929" · 74% thread
Pick your material for its % of thread, tapping RPM and the rigid-tap code.
Thread dimensions
- Major Ø
- 45.000 mm (1.7717")
- Pitch
- 4 mm
- Pitch Ø (basic)
- 42.402 mm (1.6694")
- Minor Ø (internal, basic)
- 40.670 mm (1.6012")
- Thread depth (internal)
- 2.165 mm (0.0852")
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 |
|---|---|---|---|
| 1-39/64 | 1.6094 | 40.88 | 79% |
| 41 mm | 1.6142 | 41.00 | 77% |
| 1-5/8 | 1.6250 | 41.28 | 72% |
| 41.5 mmsuggested | 1.6339 | 41.50 | 67% |
| 1-41/64 | 1.6406 | 41.67 | 64% |
| 42 mm | 1.6535 | 42.00 | 58% |
| 1-21/32 | 1.6563 | 42.07 | 56% |
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 |
|---|---|---|---|
| 1-11/16 | 1.6875 | 42.86 | 79% |
| 43 mm | 1.6929 | 43.00 | 74% |
| 1-45/64 | 1.7031 | 43.26 | 64% |
| 43.5 mm | 1.7126 | 43.50 | 55% |
3-wire measurement
- Best wire size
- 2.309 mm (0.0909")
- Over wires, at basic pitch Ø
- 45.866 mm (1.8057")
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