1-1/2-6 tap drill size
1-11/32"
- Inches
- 1.3438
- Millimetres
- 34.13
- Thread
- 72%
Drill a 1-11/32" hole before cutting a 1-1/2-6 thread. That is the standard tap drill for about 75% thread.
1-1/2-6 thread and hole sizes
| Thread | 1-1/2 diameter, 6 threads per inch, coarse (UNC) |
|---|---|
| Major diameter | 1.5000 in 38.10 mm |
| Pitch | 0.1667 in 4.233 mm |
| Tap drill, about 75% thread | 1-11/32" 1.3438 in |
| Nearest metric bit | 34.1 mm |
Why 1-11/32"
A tap cuts threads into the wall of a hole, so the hole has to be smaller than the screw. For a 1-1/2-6 thread the hole that leaves exactly 75% thread is 1.3376 in. The closest standard bit is 1-11/32" at 1.3438 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
- 1-1/2-6 tap
- 1-11/32" drill bit
- Tap and drill set
- Drill bit size gauge
- Thread pitch gauge
- Cutting oil for tapping
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