This is a bracket used to clip Screen Tight Vinyl Frame Connector to the edges of Carrera 1/24 (and 1/32) slot car track for use as a track border/wall/fence. The Vinyl connector is available at most Lowe's stores for about $4 per 8 feet section.
I've found that it works great on straights and flat curves. It works so-so on banked curves - largely because it doesn't like to twist and bend at once (to form the compound curve at the top of the banked curves). I've also only tested on the outside of curves (not the inside).
Link to Vinyl connector: https://www.lowes.com/pd/Screen-Tight-Vinyl-Frame-Connector/3024713
Inspired by this design by sjc115's Slot Car Track Wall support: https://www.thingiverse.com/thing:3434589 (Thanks for the inspiration SJC!)