1)use a plain 3mm nut and press into the thumbscrew with pliers then glue in place make sure to not get any in the thread can put a sacrificial screw while doing it to prevent this if needed

2)use a 3mm x 16-20 mm button head screw and place this though the middle of the front mount and place a small dab of ca glue to lock in place one you have determined the length you need.

3) after snapping the back into place pivot the body down onto the screw i placed chalk marker on the tip of the screw to mark the body for placement

4) ream hole in body slightly larger than screw

5) glue mount to body with e6000