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#1-72 tap drill size
Use a #53 drill (.0595 in / 1.51 mm) to tap #1-72 UNF. That gives about 75% thread engagement. Closest metric drill: 1.5 mm.
#1-72 thread specifications
| Thread | #1-72 UNF (fine) |
|---|---|
| Major (nominal) diameter | .0730 in / 1.85 mm |
| Threads per inch | 72 (pitch 0.353 mm) |
| Theoretical drill for 75% thread | .0595 in (1.51 mm) |
| Recommended tap drill | #53 = .0595 in |
Alternative drills and % of thread
Any of these drills will tap #1-72. Smaller drills give more thread but make tapping harder and raise the risk of breaking the tap, especially in stainless steel and in small sizes. 60–65% thread is common in tough materials. 75% is the general-purpose standard.
Tips for tapping #1-72
- Use cutting fluid, and with a hand tap back off about half a turn every turn or two to break the chip. Aluminium and soft materials are the exception: they tap cleanly with spiral-point taps.
- For blind holes, drill deeper than the thread you need. Allow at least 3–4 pitches beyond the last full thread for a plug tap (0.056" for 72 TPI).
- Thread engagement of 1–1.5 × the diameter (1.9–2.8 mm) is enough for most steel parts. Softer materials need more.