Put two different size screws in the two strap buttons. I've had this issue on both my 339 and the 2006 VOS LP Special I just got. Went to change out the screws so I could put Schaller strap lock buttons on and the screw that holds the stock button on the butt of the guitar is BIGGER (diameter) than the one that is closest to the neck. Not only that but the screw head on them is too big to fit down into the Schaller button so that even if you could get it on you can't get the Schaller to lock. And finding a screw with that diameter AND a head size small enough to fit into the Schaller button is virtually impossible. Looks like I have to get out the toothpicks and glue. Grrrrrrrr........