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#6-32 tap drill size
Use a #36 drill (.1065 in / 2.71 mm) to tap #6-32 UNC. That gives about 78% thread engagement. Closest metric drill: 2.7 mm.
#6-32 thread specifications
| Thread | #6-32 UNC (coarse) |
|---|---|
| Major (nominal) diameter | .1380 in / 3.50 mm |
| Threads per inch | 32 (pitch 0.794 mm) |
| Theoretical drill for 75% thread | .1076 in (2.73 mm) |
| Recommended tap drill | #36 = .1065 in |
Alternative drills and % of thread
Any of these drills will tap #6-32. 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.
| Drill | Inch | mm | % thread |
|---|---|---|---|
| #37 | .1040 in | 2.64 | 84% |
| #36 | .1065 in | 2.71 | 78% |
| 7/64 | .1094 in | 2.78 | 71% |
| #35 | .1100 in | 2.79 | 69% |
| #34 | .1110 in | 2.82 | 67% |
| #33 | .1130 in | 2.87 | 62% |
| #32 | .1160 in | 2.95 | 54% |
Tips for tapping #6-32
- 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 (0.125" for 32 TPI).
- Thread engagement of 1–1.5 × the diameter (3.5–5.3 mm) is enough for most steel parts. Softer materials need more.