5/8-18 UNF tap drill size

37/64 drill — 0.5781 in / 14.68 mm (65% thread)

Major Ø 0.6250 in · 18 threads per inch · fine series. The chart pick targets 75% thread; nearby standard drills:

Drill	Decimal (in)	mm	Thread %
19/32	0.5938	15.08	43%
37/64	0.5781	14.68	65%
9/16	0.5625	14.29	87%
35/64	0.5469	13.89	108%

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: 5/8-11 UNC