#12-32 tap drill size
#13
- Inches
- 0.1850
- Millimetres
- 4.70
- Thread
- 76%
Drill a #13 hole before cutting a #12-32 thread. That is the standard tap drill for about 75% thread.
No #13 bit? A 3/16" bit (0.1875 in) gives about 70% thread, which holds fine in most materials.
#12-32 thread and hole sizes
| Thread | #12 diameter, 32 threads per inch, extra fine (UNEF) |
|---|---|
| Major diameter | 0.2160 in 5.49 mm |
| Pitch | 0.0312 in 0.794 mm |
| Tap drill, about 75% thread | #13 0.1850 in |
| Tap drill, about 50% thread | #9 0.1960 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 | 4.7 mm |
Why #13
A tap cuts threads into the wall of a hole, so the hole has to be smaller than the screw. For a #12-32 thread the hole that leaves exactly 75% thread is 0.1856 in. The closest standard bit is #13 at 0.1850 in, which leaves 76%.
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
- #12-32 tap
- #13 drill bit
- Tap and drill set
- Drill bit size gauge
- Thread pitch gauge
- Cutting oil for tapping
As an Amazon Associate we earn from qualifying purchases. Details