#4-48 tap drill size
#42
- Inches
- 0.0935
- Millimetres
- 2.37
- Thread
- 68%
Drill a #42 hole before cutting a #4-48 thread. That is the standard tap drill for about 75% thread.
No #42 bit? A 3/32" bit (0.0938 in) gives about 67% thread, which holds fine in most materials.
#4-48 thread and hole sizes
| Thread | #4 diameter, 48 threads per inch, fine (UNF) |
|---|---|
| Major diameter | 0.1120 in 2.84 mm |
| Pitch | 0.0208 in 0.529 mm |
| Tap drill, about 75% thread | #42 0.0935 in |
| Tap drill, about 50% thread | #40 0.0980 in, for stainless and other hard materials |
| Clearance hole, close fit | #32 0.1160 in |
| Clearance hole, free fit | #30 0.1285 in |
| Nearest metric bit | 2.4 mm |
Why #42
A tap cuts threads into the wall of a hole, so the hole has to be smaller than the screw. For a #4-48 thread the hole that leaves exactly 75% thread is 0.0917 in. The closest standard bit is #42 at 0.0935 in, which leaves 68%.
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
- #4-48 tap
- #42 drill bit
- Tap and drill set
- Drill bit size gauge
- Thread pitch gauge
- Cutting oil for tapping
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