There should be a short pilot diameter at the very end of the drive screws, so just measure that and use a driil that's about .002" (0.05mm) larger. If there's no pilot diameter, try using a caliper to measure the root diameter below the "flutes" of the drive screw.
Also, when you drive them in, try to preserve the round head to keep them pretty. You can do this by measuring the radius of the head, then use a matching ball mill's tip to make a divot in the end of a soft steel punch.
Also, when you drive them in, try to preserve the round head to keep them pretty. You can do this by measuring the radius of the head, then use a matching ball mill's tip to make a divot in the end of a soft steel punch.