i have a 9/16 drill bit to drill out the oil passage on a buick block. also i had a machinist friend make a cutter with a 3/8 guide so you can get the hole stated correctly. it cant wander because you can get the hole about half way following the original hole. this really worked great and i didnt worry about the bit wandering off and putting a hole in my original block. i have no use for it now so if someone wants it i'll do $50 shipped anywhere in the 48 states.