In my case, it goes to the bolt hole for the rearmost shaft hold down bolt. The bottom of the hole is about .150” lower than the bottom of the bolt and the hole I drilled breaks through about .075 from the bottom of that hole. The rocker hold down bolt is then center drilled from the bottom to a depth that intersects the center of the rocker shaft. Finally you cross drill the bolt on one side to allow oil into the shaft.