Unified inch · UNF
#1-72 UNF 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
#53
0.0595" · 75% thread
Form tap
#51
0.0670" · 64% thread
Pick your material for its % of thread, tapping RPM and the rigid-tap code.
Thread dimensions
- Major Ø
- 0.0730" (1.854 mm)
- Threads per inch
- 72 (pitch 0.0139")
- Pitch Ø (basic)
- 0.0640" (1.625 mm)
- Minor Ø (internal, basic)
- 0.0580" (1.472 mm)
- Thread depth (internal)
- 0.0075" (0.191 mm)
Basic sizes of the 60° form. Tolerance classes (2B/3B) 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 |
|---|---|---|---|
| 1.5 mm | 0.0591 | 1.50 | 77% |
| #53 | 0.0595 | 1.51 | 75% |
| 1/16 | 0.0625 | 1.59 | 58% |
| 1.6 mm | 0.0630 | 1.60 | 55% |
| #52 | 0.0635 | 1.61 | 53% |
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 |
|---|---|---|---|
| 1.7 mm | 0.0669 | 1.70 | 64% |
| #51 | 0.0670 | 1.70 | 64% |
3-wire measurement
- Best wire size
- 0.0080" (0.204 mm)
- Over wires, at basic pitch Ø
- 0.0760" (1.931 mm)
For the external thread (the screw). The best wire touches the flanks at the pitch diameter.
Sources
- ASME B1.1 — Unified Inch Screw Threads (UN and UNR thread form)
- 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