3/4-10 Tap Drill Size and Drill Bit Size
Use a 21/32 drill bit
3/4-10 · 0.6563 in / 16.67 mm · ~75% thread
3/4-10 is a large coarse UNC thread. A 21/32 inch bit is the standard tap drill for strong 75% thread engagement.
At a glance
| Tap drill | 21/32 |
|---|---|
| Inches | 0.6563 in |
| Millimetres | 16.67 mm |
| Major diameter | 0.75 in |
| Pitch | 0.1 in |
| Threads per inch | 10 |
Why this size
drillØ = major − (pitch × %thread) = 0.75 − (0.1 × 0.75) = 0.6750 in → next standard drill 21/32 (0.6563 in / 16.67 mm)
At this size, drilling the pilot correctly prevents tap breakage. 21/32 in gives a solid 75% thread.
Clearance holes for 3/4-10
A clearance hole lets the bolt pass through unthreaded – close fit keeps parts aligned, free fit allows movement.
| Tap drill (cuts threads) | 21/32 |
|---|---|
| Close fit clearance | 25/32 bit |
| Free fit clearance | 29/32 bit |
Related sizes
Compare with adjacent threads – coarse, fine and the opposite measurement system: