I created a simple machine vise work stop clamp.

The dowels are a press fit into the clamp. For the thread you can either tap threads with a m5 tap or just thread the screw straight into the plastic. The spring i used was just something i found in a drawer i had had laying around. any spring that can fit over the screw should work.

(1) M5 x 30mm socket head cap screw
(2) 3mm x 40mm dowel pins
(1) spring 25mm long id=5.4mm od 6.5mm