8-32 Tap Drill Size and Drill Bit to Use
Use a #29 drill bit
8-32 · 0.136 in / 3.45 mm · ~75% thread
8-32 is a common small UNC machine screw thread in fixtures, brackets and hardware. A #29 bit is the standard tap drill for a 75% fit.
At a glance
| Tap drill | #29 |
|---|---|
| Inches | 0.136 in |
| Millimetres | 3.45 mm |
| Major diameter | 0.164 in |
| Pitch | 0.0313 in |
| Threads per inch | 32 |
Why this size
drillØ = major − (pitch × %thread) = 0.164 − (0.0313 × 0.75) = 0.1405 in → next standard drill #29 (0.136 in / 3.45 mm)
The #29 is the tap drill for a proper 8-32 thread. For a clearance hole (bolt passes through unthreaded) a #15 bit is the close fit.
Clearance holes for 8-32
A clearance hole lets the bolt pass through unthreaded – close fit keeps parts aligned, free fit allows movement.
| Tap drill (cuts threads) | #29 |
|---|---|
| Close fit clearance | #15 bit |
| Free fit clearance | #3 bit |
Related sizes
Compare with adjacent threads – coarse, fine and the opposite measurement system: