Y drill bit size

Y drill = .4040 in = 10.26 mm. Closest metric drill: 10.3 mm.

Nearby drill sizes

Drill	Type	Inch	mm	Difference
V	letter	.3770 in	9.576	-27.0 thou
W	letter	.3860 in	9.804	-18.0 thou
25/64	fraction	.3906 in	9.922	-13.4 thou
X	letter	.3970 in	10.084	-7.0 thou
Y	letter	.4040 in	10.262	0.0 thou
13/32	fraction	.4063 in	10.319	2.2 thou
Z	letter	.4130 in	10.490	9.0 thou
27/64	fraction	.4219 in	10.716	17.9 thou
7/16	fraction	.4375 in	11.112	33.5 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.