#6-32 tap drill size
#36
- Inches
- 0.1065
- Millimetres
- 2.71
- Thread
- 78%
Drill a #36 hole before cutting a #6-32 thread. That is the standard tap drill for about 75% thread.
No #36 bit? A 7/64" bit (0.1094 in) gives about 71% thread, which holds fine in most materials.
#6-32 thread and hole sizes
| Thread | #6 diameter, 32 threads per inch, coarse (UNC) |
|---|---|
| Major diameter | 0.1380 in 3.51 mm |
| Pitch | 0.0312 in 0.794 mm |
| Tap drill, about 75% thread | #36 0.1065 in |
| Tap drill, about 50% thread | #32 0.1160 in, for stainless and other hard materials |
| Clearance hole, close fit | #27 0.1440 in |
| Clearance hole, free fit | #25 0.1495 in |
| Nearest metric bit | 2.7 mm |
Why #36
A tap cuts threads into the wall of a hole, so the hole has to be smaller than the screw. For a #6-32 thread the hole that leaves exactly 75% thread is 0.1076 in. The closest standard bit is #36 at 0.1065 in, which leaves 78%.
More thread than that adds almost no strength and makes the tap much easier to break. In hard or tough material, go one step larger.
Some charts list #35 (0.1100 in) for #6-32. That gives about 69% thread and also works; #36 is the more common listing.
Tools for this job
- #6-32 tap
- #36 drill bit
- Tap and drill set
- Drill bit size gauge
- Thread pitch gauge
- Cutting oil for tapping
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