Quickie: Screw size for Vertical Bottle Adaptor?

[Patron God of Pirates]

Question:
What size screw is used for a vertical bottle adaptor?

Reason:
I making a custom rail extention and I need to know what size hole to drill for the screw.

Thanx
-Zach

[Big'n slo]

Takes a 1/4 x 20 thread
#8 or #9 drill

[Patron God of Pirates]

-Thanx