ISO metric · fine
M36 × 3 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
33.5 mm
1.3189" · 64% thread
Or 1-5/16 (1.3125") for 68%
Form tap
34.5 mm
1.3583" · 74% thread
Pick your material for its % of thread, tapping RPM and the rigid-tap code.
Thread dimensions
- Major Ø
- 36.000 mm (1.4173")
- Pitch
- 3 mm
- Pitch Ø (basic)
- 34.051 mm (1.3406")
- Minor Ø (internal, basic)
- 32.752 mm (1.2895")
- Thread depth (internal)
- 1.624 mm (0.0639")
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 |
|---|---|---|---|
| 1-19/64 | 1.2969 | 32.94 | 79% |
| 33 mm | 1.2992 | 33.00 | 77% |
| 1-5/16suggested | 1.3125 | 33.34 | 68% |
| 33.5 mm | 1.3189 | 33.50 | 64% |
| 1-21/64 | 1.3281 | 33.73 | 58% |
| 34 mm | 1.3386 | 34.00 | 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 |
|---|---|---|---|
| 34.5 mm | 1.3583 | 34.50 | 74% |
| 1-23/64 | 1.3594 | 34.53 | 72% |
| 1-3/8 | 1.3750 | 34.93 | 53% |
3-wire measurement
- Best wire size
- 1.732 mm (0.0682")
- Over wires, at basic pitch Ø
- 36.650 mm (1.4429")
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