From:Mark Hill
Subject:counter bore to the thread Date:Sun Mar 3 21:17:55 2013
This was a tricky thing, if you look the threads dont start until about .500 in from the edge of the case. The counterbore is 1.375 in diam. This had to be bored after the tap drill size so the tap would start right. The counterbore centers the oil pan to the rest of the case.