I have always drilled my pilot holes for pad screws at about 0.5mm more than the shank diameter of the screw, depending on the screw it seems to be 3mm or 4mm or between. I just want a balance between being easy enough to put in but not so easy the threads don't have enough to grip on. If you are worried about drilling too big a hole then drill a small hole say 2.5mm for fitting screws and just use some normal short household screws, the supplied screws are sightly fatter and courser so once fitted you could drill the holes out to 3mm or whatever it needs to be and use them for the final job.

On this thread ( which has gone a bit dead because i have not done anything with this gun for a while ) I install a silvers pad and you can see how it works for me.

http://www.doublegunshop.com/forums/ubbt...1168#Post421168

If you are really worried that you are going to be taking the pad on and off that many times order two bolts and two threaded inserts, by fitting the threaded inserts you can back your bolts in and out as much as you like with no issues.