1-8 UNC tap drill size

7/8 drill — 0.8750 in / 22.22 mm (77% thread)

Major Ø 1.0000 in · 8 threads per inch · coarse series. The chart pick targets 75% thread; nearby standard drills:

Drill	Decimal (in)	mm	Thread %
29/32	0.9063	23.02	58%
57/64	0.8906	22.62	67%
7/8	0.8750	22.22	77%
55/64	0.8594	21.83	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, fine series: 1-12 UNF