Quick answer
For a #10-24 UNC tap, use a #25 drill bit. The decimal equivalent is about 0.1495 inches, or roughly 3.80 mm.
Thread
#10-24 UNC
Tap drill
#25 drill bit
Decimal size
0.1495 in
Close metric size
3.80 mm
Why #25 is used
The #25 bit gives a practical thread depth for a #10-24 coarse machine screw while leaving room for the tap to cut cleanly.
Before you drill
Confirm that the screw is #10-24 and not #10-32. The diameter is similar, but the thread pitch is different, so the tap drill size changes.
Useful tools for this job
A numbered drill bit index is useful here because many tap drill sizes use numbered bits rather than common fractional bits.
Frequently asked questions
Can I use a 5/32 inch bit for a #10-24 tap?
5/32 inch is larger than the standard #25 tap drill. It may work for a looser thread, but #25 is the standard starting point.
Is #10-24 coarse or fine thread?
#10-24 is coarse thread. #10-32 is the common fine-thread version.