5/16-32 tap drill size
9/32"
- Inches
- 0.2812
- Millimetres
- 7.14
- Thread
- 77%
Drill a 9/32" hole before cutting a 5/16-32 thread. That is the standard tap drill for about 75% thread.
5/16-32 thread and hole sizes
| Thread | 5/16 diameter, 32 threads per inch, extra fine (UNEF) |
|---|---|
| Major diameter | 0.3125 in 7.94 mm |
| Pitch | 0.0312 in 0.794 mm |
| Tap drill, about 75% thread | 9/32" 0.2812 in |
| Tap drill, about 50% thread | Letter L 0.2900 in, for stainless and other hard materials |
| Clearance hole, close fit | Letter P 0.3230 in |
| Clearance hole, free fit | Letter Q 0.3320 in |
| Nearest metric bit | 7.1 mm |
Why 9/32"
A tap cuts threads into the wall of a hole, so the hole has to be smaller than the screw. For a 5/16-32 thread the hole that leaves exactly 75% thread is 0.2821 in. The closest standard bit is 9/32" at 0.2812 in, which leaves 77%.
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
- 5/16-32 tap
- 9/32" drill bit
- Tap and drill set
- Drill bit size gauge
- Thread pitch gauge
- Cutting oil for tapping
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