This fitting allows for a -4 oil feed line to be installed below the oil pressure sender. This is the easiest oil source for adding a turbo to a factory non turbo redblock. The usual oil source in the front of be block requires much more disassembly and requires removing a pipe plug from the front of the block. Those pipe plugs are often quite reluctant to move, this is a great option if you have a stripped plug or don't wish to battle with it at all.
