#12-24 tap drill size
#16
- Inches
- 0.1770
- Millimetres
- 4.50
- Thread
- 72%
Drill a #16 hole before cutting a #12-24 thread. That is the standard tap drill for about 75% thread.
No #16 bit? A 11/64" bit (0.1719 in) gives about 82% thread, which holds fine in most materials.
#12-24 thread and hole sizes
| Thread | #12 diameter, 24 threads per inch, coarse (UNC) |
|---|---|
| Major diameter | 0.2160 in 5.49 mm |
| Pitch | 0.0417 in 1.058 mm |
| Tap drill, about 75% thread | #16 0.1770 in |
| Tap drill, about 50% thread | #12 0.1890 in, for stainless and other hard materials |
| Clearance hole, close fit | #2 0.2210 in |
| Clearance hole, free fit | #1 0.2280 in |
| Nearest metric bit | 4.5 mm |
Why #16
A tap cuts threads into the wall of a hole, so the hole has to be smaller than the screw. For a #12-24 thread the hole that leaves exactly 75% thread is 0.1754 in. The closest standard bit is #16 at 0.1770 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
- #12-24 tap
- #16 drill bit
- Tap and drill set
- Drill bit size gauge
- Thread pitch gauge
- Cutting oil for tapping
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