Unified inch · UNF
#0-80 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
3/64
0.0469" · 81% thread
Form tap
#54
0.0550" · 59% thread
Pick your material for its % of thread, tapping RPM and the rigid-tap code.
Thread dimensions
- Major Ø
- 0.0600" (1.524 mm)
- Threads per inch
- 80 (pitch 0.0125")
- Pitch Ø (basic)
- 0.0519" (1.318 mm)
- Minor Ø (internal, basic)
- 0.0465" (1.180 mm)
- Thread depth (internal)
- 0.0068" (0.172 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 |
|---|---|---|---|
| #56 | 0.0465 | 1.18 | 83% |
| 3/64 | 0.0469 | 1.19 | 81% |
| 1.2 mm | 0.0472 | 1.20 | 79% |
| 1.3 mm | 0.0512 | 1.30 | 54% |
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 |
|---|---|---|---|
| #54 | 0.0550 | 1.40 | 59% |
| 1.4 mm | 0.0551 | 1.40 | 57% |
3-wire measurement
- Best wire size
- 0.0072" (0.183 mm)
- Over wires, at basic pitch Ø
- 0.0627" (1.593 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