#2-56 tap drill size
#50
- Inches
- 0.0700
- Millimetres
- 1.78
- Thread
- 69%
Drill a #50 hole before cutting a #2-56 thread. That is the standard tap drill for about 75% thread.
#2-56 thread and hole sizes
| Thread | #2 diameter, 56 threads per inch, coarse (UNC) |
|---|---|
| Major diameter | 0.0860 in 2.18 mm |
| Pitch | 0.0179 in 0.454 mm |
| Tap drill, about 75% thread | #50 0.0700 in |
| Tap drill, about 50% thread | #49 0.0730 in, for stainless and other hard materials |
| Clearance hole, close fit | #43 0.0890 in |
| Clearance hole, free fit | #41 0.0960 in |
| Nearest metric bit | 1.8 mm |
Why #50
A tap cuts threads into the wall of a hole, so the hole has to be smaller than the screw. For a #2-56 thread the hole that leaves exactly 75% thread is 0.0686 in. The closest standard bit is #50 at 0.0700 in, which leaves 69%.
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
- #2-56 tap
- #50 drill bit
- Tap and drill set
- Drill bit size gauge
- Thread pitch gauge
- Cutting oil for tapping
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