Dont know if this helps any but if you are drilling for a bulkhead the breakdown is

1/2 bulkhead-1 1/8 Diam hole
3/4 bulkhead-1 7/16 to 1 1/2 diam. hole
1 in bulkhead-1 3/4 diam hole

from what I have seen they normally do not sell these at HD or LOWES .. Look on gl*******s.com they sell them there for a real good price..