Plexiglass railing holder for plywood.

thingiverse

This rounded clip holds Optix 0.09" plexiglass vertically, and is intended to be screwed to plywood. This is currently being used on an overhead HO scale model train track, to prevent derailments from becoming something truly horrific -- after all, HO is 1:87 scale, so an 80" drop in the real world is a scale 580 foot drop -- not something ANYTHING is likely to survive, much less a locomotive or rolling stock. Secure to plywood with Spax #6 0.5" multipurpose construction screws -- the screws usually run just over $2 for a box of 50 at whatever big box hardware store is nearby. The plexiglass just sets into the top clip -- gravity holds it in place.