3/8-24 UNF tap drill size

Q drill — 0.3320 in / 8.43 mm (79% thread)

Major Ø 0.3750 in · 24 threads per inch · fine series. The chart pick targets 75% thread; nearby standard drills:

Drill	Decimal (in)	mm	Thread %
11/32	0.3438	8.73	58%
R	0.3390	8.61	67%
Q	0.3320	8.43	79%
21/64	0.3281	8.33	87%

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: 3/8-16 UNC