7/16-14 tap drill size
Letter U
- Inches
- 0.3680
- Millimetres
- 9.35
- Thread
- 75%
Drill a Letter U hole before cutting a 7/16-14 thread. That is the standard tap drill for about 75% thread.
No Letter U bit? A 3/8" bit (0.3750 in) gives about 67% thread, which holds fine in most materials.
7/16-14 thread and hole sizes
| Thread | 7/16 diameter, 14 threads per inch, coarse (UNC) |
|---|---|
| Major diameter | 0.4375 in 11.11 mm |
| Pitch | 0.0714 in 1.814 mm |
| Tap drill, about 75% thread | Letter U 0.3680 in |
| Tap drill, about 50% thread | 25/64" 0.3906 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 | 9.3 mm |
Why Letter U
A tap cuts threads into the wall of a hole, so the hole has to be smaller than the screw. For a 7/16-14 thread the hole that leaves exactly 75% thread is 0.3679 in. The closest standard bit is Letter U at 0.3680 in, which leaves 75%.
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
- 7/16-14 tap
- Letter U drill bit
- Tap and drill set
- Drill bit size gauge
- Thread pitch gauge
- Cutting oil for tapping
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