I'm mounting my WTK metal disks by drillling a 1/8" hole where I want the disk mounted. Then I start a 1" 8x32 screw from the inside of the box. It's difficult but it can be done and screw it home from the inside. Then I push the disk on the end of the screw from the outside of the box. The hole on the disk is tight for an 8x32 screw but it works. After that I start an 8X32 wing nut on the screw and tighten it forcing the disk all the way to the wood. To adjust the entrance just loosen the wing nut 1/2 a turn and turn the disk then retighten the wing nut.
I know I could do it cheaper. Anybody have a better or different idea?