The square-headed oil drain plug in my 17.5HP B&S engined lawn tractor has rounded off over time and my 12 point socket no longer works. I think I should be able to use a 4 point socket. What size is the head on the drain plug (size of 4 point socket)? And what are the threads on the plug? I'm going to replace the plug but don't want to use the B&S plug again; I want something with a hex head if possible. Thanks.