#10-24 tap drill size
#25
- Inches
- 0.1495
- Millimetres
- 3.80
- Thread
- 75%
Drill a #25 hole before cutting a #10-24 thread. That is the standard tap drill for about 75% thread.
No #25 bit? A 5/32" bit (0.1562 in) gives about 62% thread, which holds fine in most materials.
#10-24 thread and hole sizes
| Thread | #10 diameter, 24 threads per inch, coarse (UNC) |
|---|---|
| Major diameter | 0.1900 in 4.83 mm |
| Pitch | 0.0417 in 1.058 mm |
| Tap drill, about 75% thread | #25 0.1495 in |
| Tap drill, about 50% thread | #20 0.1610 in, for stainless and other hard materials |
| Clearance hole, close fit | #9 0.1960 in |
| Clearance hole, free fit | #7 0.2010 in |
| Nearest metric bit | 3.8 mm |
Why #25
A tap cuts threads into the wall of a hole, so the hole has to be smaller than the screw. For a #10-24 thread the hole that leaves exactly 75% thread is 0.1494 in. The closest standard bit is #25 at 0.1495 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
- #10-24 tap
- #25 drill bit
- Tap and drill set
- Drill bit size gauge
- Thread pitch gauge
- Cutting oil for tapping
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