1-1/4-12 tap drill size
1-11/64"
- Inches
- 1.1719
- Millimetres
- 29.77
- Thread
- 72%
Drill a 1-11/64" hole before cutting a 1-1/4-12 thread. That is the standard tap drill for about 75% thread.
1-1/4-12 thread and hole sizes
| Thread | 1-1/4 diameter, 12 threads per inch, fine (UNF) |
|---|---|
| Major diameter | 1.2500 in 31.75 mm |
| Pitch | 0.0833 in 2.117 mm |
| Tap drill, about 75% thread | 1-11/64" 1.1719 in |
| Nearest metric bit | 29.8 mm |
Why 1-11/64"
A tap cuts threads into the wall of a hole, so the hole has to be smaller than the screw. For a 1-1/4-12 thread the hole that leaves exactly 75% thread is 1.1688 in. The closest standard bit is 1-11/64" at 1.1719 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
- 1-1/4-12 tap
- 1-11/64" 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