10-24 Tap Drill Size and Correct Drill Bit
Use a #25 drill bit
10-24 · 0.1495 in / 3.8 mm · ~75% thread
10-24 is the coarse UNC version of the #10 machine screw. A #25 bit is the correct tap drill for a strong 75% thread.
At a glance
| Tap drill | #25 |
|---|---|
| Inches | 0.1495 in |
| Millimetres | 3.8 mm |
| Major diameter | 0.19 in |
| Pitch | 0.0417 in |
| Threads per inch | 24 |
Why this size
drillØ = major − (pitch × %thread) = 0.19 − (0.0417 × 0.75) = 0.1587 in → next standard drill #25 (0.1495 in / 3.8 mm)
Don't confuse 10-24 (coarse, #25 bit) with 10-32 (fine, #21 bit). The pitch differs and so does the correct drill.
Clearance holes for 10-24
A clearance hole lets the bolt pass through unthreaded – close fit keeps parts aligned, free fit allows movement.
| Tap drill (cuts threads) | #25 |
|---|---|
| Close fit clearance | #5 bit |
| Free fit clearance | B bit |
Related sizes
Compare with adjacent threads – coarse, fine and the opposite measurement system: