1-12 tap drill size
59/64"
- Inches
- 0.9219
- Millimetres
- 23.42
- Thread
- 72%
Drill a 59/64" hole before cutting a 1-12 thread. That is the standard tap drill for about 75% thread.
1-12 thread and hole sizes
| Thread | 1 diameter, 12 threads per inch, fine (UNF) |
|---|---|
| Major diameter | 1.0000 in 25.40 mm |
| Pitch | 0.0833 in 2.117 mm |
| Tap drill, about 75% thread | 59/64" 0.9219 in |
| Tap drill, about 50% thread | 61/64" 0.9531 in, for stainless and other hard materials |
| Clearance hole, close fit | 1-1/64" 1.0156 in |
| Clearance hole, free fit | 1-1/32" 1.0312 in |
| Nearest metric bit | 23.4 mm |
Why 59/64"
A tap cuts threads into the wall of a hole, so the hole has to be smaller than the screw. For a 1-12 thread the hole that leaves exactly 75% thread is 0.9188 in. The closest standard bit is 59/64" at 0.9219 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.
Some charts list 15/16" for 1-12. That leaves only about 58% thread, so 59/64" is the better choice for a full-strength thread.
Tools for this job
- 1-12 tap
- 59/64" drill bit
- Tap and drill set
- Drill bit size gauge
- Thread pitch gauge
- Cutting oil for tapping
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