3/8-16 UNC tap drill size

5/16 drill — 0.3125 in / 7.94 mm (77% thread)

Major Ø 0.3750 in · 16 threads per inch · coarse series. The chart pick targets 75% thread; nearby standard drills:

Drill	Decimal (in)	mm	Thread %
P	0.3230	8.20	64%
O	0.3160	8.03	73%
5/16	0.3125	7.94	77%
N	0.3020	7.67	90%

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, fine series: 3/8-24 UNF