ISO metric · fine
M48 × 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
45.5 mm
1.7913" · 64% thread
Form tap
46.5 mm
1.8307" · 74% thread
Pick your material for its % of thread, tapping RPM and the rigid-tap code.
Thread dimensions
- Major Ø
- 48.000 mm (1.8898")
- Pitch
- 3 mm
- Pitch Ø (basic)
- 46.051 mm (1.8130")
- Minor Ø (internal, basic)
- 44.752 mm (1.7619")
- 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 |
|---|---|---|---|
| 1-49/64 | 1.7656 | 44.85 | 81% |
| 45 mm | 1.7717 | 45.00 | 77% |
| 1-25/32 | 1.7813 | 45.24 | 71% |
| 45.5 mm | 1.7913 | 45.50 | 64% |
| 1-51/64 | 1.7969 | 45.64 | 61% |
| 46 mm | 1.8110 | 46.00 | 51% |
| 1-13/16 | 1.8125 | 46.04 | 50% |
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 |
|---|---|---|---|
| 1-53/64 | 1.8281 | 46.43 | 77% |
| 46.5 mm | 1.8307 | 46.50 | 74% |
| 1-27/32 | 1.8438 | 46.83 | 57% |
3-wire measurement
- Best wire size
- 1.732 mm (0.0682")
- Over wires, at basic pitch Ø
- 48.650 mm (1.9153")
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