13/16 inch in mm and decimal

13/16 in = 0.8125 in = 20.637 mm. Closest metric drill: 20 mm.

Taps that use a 13/16 drill

Drill	Type	Inch	mm	Difference
3/4	fraction	.7500 in	19.050	-62.5 thou
49/64	fraction	.7656 in	19.447	-46.9 thou
25/32	fraction	.7813 in	19.844	-31.3 thou
51/64	fraction	.7969 in	20.241	-15.6 thou
13/16	fraction	.8125 in	20.637	0.0 thou
53/64	fraction	.8281 in	21.034	15.6 thou
27/32	fraction	.8438 in	21.431	31.3 thou
55/64	fraction	.8594 in	21.828	46.9 thou
7/8	fraction	.8750 in	22.225	62.5 thou

1 thou = 0.001 in = 0.0254 mm. Drills a few thou apart are usually interchangeable for clearance holes, but not for tap drills or reamer pilots.