The following table shows the tap drill and clearance drill bit sizes to use with various screw sizes that are commonly used in robot building. Keeping this information handy can save you some while you build.

Screw Tap Drill Clearance Drill
2-256 .070 (#50) .089 (#43)
4-40 .089 (#43) .116 (#32)
6-32 .106 (#36) .144 (#27)
8-32 .136 (#29) .170 (#18)
10-32 .159 (#21) .196 (#9)