#16 Drill Bit Size and Diameter
A #16 drill bit measures 0.1770 in
4.50 mm · number-size drill · between 11/64 in and #15
The #16 is a numbered drill bit in the American gauge series, measuring 0.1770 inches (4.50 mm). It sits between an 11/64 in bit (0.1719 in) and a #15 bit (0.1800 in). It is best known as the standard tap drill for a 12-24 UNC thread, and it also serves pilot and clearance work near 3/16 in.
At a glance
| Drill size | #16 |
|---|---|
| Diameter | 0.1770 in |
| Millimetres | 4.50 mm |
| Series | Number drill (gauge) 1–97 |
| Closest fractional | 11/64 in (0.1719 in, slightly smaller) |
What the #16 is used for
12-24 tap drill: drillØ = major − (pitch × 0.75) = 0.2160 − (0.0417 × 0.75) = 0.1848 in → next standard bit = #16 (0.1770 in)
A #16 hole before a 12-24 tap gives the standard ~75% thread engagement. For 10-24 and 10-32 tapping the smaller #25 and #21 bits are correct — related cards below. Outside tapping, the #16 is a practical pilot/clearance size near 3/16 in.
Related sizes
Other number drill bits
The neighbourhood of the #16 in the gauge series: