Holley fuel bowl thread tap

I can't guarantee that there is only one float bowl stud / screw size on all Holley carbs so use this info at your own risk.

based on the below website It looks like 12-24 is what you need

ARP Carburetor Float Bowl Bolt Kits 400-0310

DEWALT #16 Drill and 12-24 NC Tap Set-DWA1408 - The Home Depot

unless the hole is a through hole you should look for a "bottom tap" with the flat end