OK, tell me if I'm losing my mind. So I need and cant find a 5/16 socket. Go to the hardware store, buy 5/16 socket, socket is too big for 5/16 hex head machine screw. 5/16 wrench fits perfect so I know it's 5/16. Go back to hardware store with screw. None of the standard 5/16 sockets fit. But the 5/16 deep socket fits. So I tell the old guy who works there "Hey, these things must be mismarked or something because they don't fit." He says, "No, the 5/16 socket is a 12 point socket and that is a different size than the six point deep socket" Now I figure the guy that's worked 50 years in the hardware store probably has forgotten more about hardware and tools than I'll ever know, but how the hell is a socket any bigger or smaller based on the number of points? Why isn't 5/16 of an inch 5/16 or an inch no matter what?