3/4-10 tap drill size
21/32"
- Inches
- 0.6562
- Millimetres
- 16.67
- Thread
- 72%
Drill a 21/32" hole before cutting a 3/4-10 thread. That is the standard tap drill for about 75% thread.
3/4-10 thread and hole sizes
| Thread | 3/4 diameter, 10 threads per inch, coarse (UNC) |
|---|---|
| Major diameter | 0.7500 in 19.05 mm |
| Pitch | 0.1000 in 2.540 mm |
| Tap drill, about 75% thread | 21/32" 0.6562 in |
| Tap drill, about 50% thread | 11/16" 0.6875 in, for stainless and other hard materials |
| Clearance hole, close fit | 49/64" 0.7656 in |
| Clearance hole, free fit | 25/32" 0.7812 in |
| Nearest metric bit | 16.7 mm |
Why 21/32"
A tap cuts threads into the wall of a hole, so the hole has to be smaller than the screw. For a 3/4-10 thread the hole that leaves exactly 75% thread is 0.6526 in. The closest standard bit is 21/32" at 0.6562 in, which leaves 72%.
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.
Tools for this job
- 3/4-10 tap
- 21/32" drill bit
- Tap and drill set
- Drill bit size gauge
- Thread pitch gauge
- Cutting oil for tapping
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