#10-32 UNF tap drill size

#21 drill — 0.1590 in / 4.04 mm (76% thread)

Major Ø 0.1900 in · 32 threads per inch · fine series. The chart pick targets 75% thread; nearby standard drills:

Drill	Decimal (in)	mm	Thread %
#20	0.1610	4.09	71%
#21	0.1590	4.04	76%
#22	0.1570	3.99	81%
5/32	0.1563	3.97	83%

Cut taps only — roll-form taps need a larger hole. 65–75% suits general work; drop toward 55% in tough material. Verify before you cut.

Same size, coarse series: #10-24 UNC