#25 Drill Bit Size and Diameter
A #25 drill bit measures 0.1495 in
3.80 mm · number-size drill · used as the 10-24 tap drill
The #25 is a numbered drill bit in the American gauge series, measuring 0.1495 inches (3.80 mm). It sits between a 9/64 in bit (0.1406 in) and a #24 bit (0.1520 in). It is best known as the standard tap drill for a 10-24 UNC coarse thread.
At a glance
| Drill size | #25 |
|---|---|
| Diameter | 0.1495 in |
| Millimetres | 3.80 mm |
| Series | Number drill (gauge) 1–97 |
| Closest fractional | 9/64 in (0.1406 in, slightly smaller) |
What the #25 is used for
10-24 tap drill: drillØ = major − (pitch × 0.75) = 0.1900 − (0.0417 × 0.75) = 0.1587 in → nearest standard bit = #25 (0.1495 in)
A #25 hole before a 10-24 tap gives the standard ~75% thread engagement. Do not confuse it with the 10-32 fine thread, which uses a #21 bit.
Related sizes
Other number drill bits
The neighbourhood of the #25 in the gauge series: