I've pinned my Benelli M4 collapsible stock. This is how I did it FYI.
1) Remove button from stock assembly.
2) Drill (through button) and tap for a 4-48 set screw. Tap only deep enough to let set screw be flush with top of button
3) Re assemble stock and position it to your preferred LOP
4) Drop a 3/32 dia pin into tapped hole. Length of pin determined by length of set screw your using.
5) Install set screw
6) Done