O Drill Size

A O letter drill is 0.3160" (8.026 mm).

Closest fraction: 5/16 (0.3125", under by 0.0035").

Next size down / up

Drill	Inch	mm
8 mm	0.3150	8.000
P	0.3230	8.204

Printable PDF version - Drill Size Chart
Clean letter-size sheet for the toolbox or shop wall. Instant download, $3.49.