#3-48 tap drill size
#47
- Inches
- 0.0785
- Millimetres
- 1.99
- Thread
- 76%
Drill a #47 hole before cutting a #3-48 thread. That is the standard tap drill for about 75% thread.
No #47 bit? A 5/64" bit (0.0781 in) gives about 77% thread, which holds fine in most materials.
#3-48 thread and hole sizes
| Thread | #3 diameter, 48 threads per inch, coarse (UNC) |
|---|---|
| Major diameter | 0.0990 in 2.51 mm |
| Pitch | 0.0208 in 0.529 mm |
| Tap drill, about 75% thread | #47 0.0785 in |
| Tap drill, about 50% thread | #44 0.0860 in, for stainless and other hard materials |
| Clearance hole, close fit | #37 0.1040 in |
| Clearance hole, free fit | #35 0.1100 in |
| Nearest metric bit | 2 mm |
Why #47
A tap cuts threads into the wall of a hole, so the hole has to be smaller than the screw. For a #3-48 thread the hole that leaves exactly 75% thread is 0.0787 in. The closest standard bit is #47 at 0.0785 in, which leaves 76%.
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
- #3-48 tap
- #47 drill bit
- Tap and drill set
- Drill bit size gauge
- Thread pitch gauge
- Cutting oil for tapping
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