7/16-20 tap drill size
25/64"
- Inches
- 0.3906
- Millimetres
- 9.92
- Thread
- 72%
Drill a 25/64" hole before cutting a 7/16-20 thread. That is the standard tap drill for about 75% thread.
7/16-20 thread and hole sizes
| Thread | 7/16 diameter, 20 threads per inch, fine (UNF) |
|---|---|
| Major diameter | 0.4375 in 11.11 mm |
| Pitch | 0.0500 in 1.270 mm |
| Tap drill, about 75% thread | 25/64" 0.3906 in |
| Tap drill, about 50% thread | 13/32" 0.4062 in, for stainless and other hard materials |
| Clearance hole, close fit | 29/64" 0.4531 in |
| Clearance hole, free fit | 15/32" 0.4688 in |
| Nearest metric bit | 9.9 mm |
Why 25/64"
A tap cuts threads into the wall of a hole, so the hole has to be smaller than the screw. For a 7/16-20 thread the hole that leaves exactly 75% thread is 0.3888 in. The closest standard bit is 25/64" at 0.3906 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
- 7/16-20 tap
- 25/64" drill bit
- Tap and drill set
- Drill bit size gauge
- Thread pitch gauge
- Cutting oil for tapping
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