S drill bit size

S drill = .3480 in = 8.84 mm. Closest metric drill: 8.8 mm.

Nearby drill sizes

Drill	Type	Inch	mm	Difference
21/64	fraction	.3281 in	8.334	-19.9 thou
Q	letter	.3320 in	8.433	-16.0 thou
R	letter	.3390 in	8.611	-9.0 thou
11/32	fraction	.3438 in	8.731	-4.2 thou
S	letter	.3480 in	8.839	0.0 thou
T	letter	.3580 in	9.093	10.0 thou
23/64	fraction	.3594 in	9.128	11.4 thou
U	letter	.3680 in	9.347	20.0 thou
3/8	fraction	.3750 in	9.525	27.0 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.