MoJo JoJoe wrote
...assuming the screw head fits and the problem is the threaded shaft of the screw).
Yeah, you got it. The screw head will fit inside the lug, but the threaded shaft is too big for the drilled hole at the bottom of the lug. The standard screws my Studio came with are slightly smaller than the screws used in the R9, and so fitted fine without me having to use the really thin Schaller screws when I originally fitted the Schallers to my Studio.
I'm going to try drilling the lug first using a new drillbit and hopefully without damaging it, as this will be a quick win and also allow me to leave the holes and screws going into the guitar standard. If I mess up the lug or just generally don't come right, I'll buy a new lock/lug and do it Alan's way.
Thanks for the tip re the Fender felt thingys. Any idea where I can get some?