5/16-24 UNF tap drill size

I drill — 0.2720 in / 6.91 mm (75% thread)

Major Ø 0.3125 in · 24 threads per inch · fine series. The chart pick targets 75% thread; nearby standard drills:

Drill	Decimal (in)	mm	Thread %
J	0.2770	7.04	66%
I	0.2720	6.91	75%
H	0.2660	6.76	86%
17/64	0.2656	6.75	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: 5/16-18 UNC