#8-32 tap drill size
#29
- Inches
- 0.1360
- Millimetres
- 3.45
- Thread
- 69%
Drill a #29 hole before cutting a #8-32 thread. That is the standard tap drill for about 75% thread.
#8-32 thread and hole sizes
| Thread | #8 diameter, 32 threads per inch, coarse (UNC) |
|---|---|
| Major diameter | 0.1640 in 4.17 mm |
| Pitch | 0.0312 in 0.794 mm |
| Tap drill, about 75% thread | #29 0.1360 in |
| Tap drill, about 50% thread | #27 0.1440 in, for stainless and other hard materials |
| Clearance hole, close fit | #18 0.1695 in |
| Clearance hole, free fit | #16 0.1770 in |
| Nearest metric bit | 3.5 mm |
Why #29
A tap cuts threads into the wall of a hole, so the hole has to be smaller than the screw. For a #8-32 thread the hole that leaves exactly 75% thread is 0.1336 in. The closest standard bit is #29 at 0.1360 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
- #8-32 tap
- #29 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