This is an end-stop made to fit Kreg Mini-T-Track. The 'mini' is a low-profile 3/8" deep t-track. The end stop has a hole designed to fit an M3x4mm Socket or Button head screw.

This is designed to cover the sharp metal edges of the t-track and to give the ends a nice finished look. Since I didn't need a lot of holding strength I used some blue PLA I had laying around that was a close match.

PETG might be a better choice if you want to screw the end stop down tight enough to prevent stuff from sliding out. In that case I might remove the countersink for the screw head and switch to a M3x5mm grub screw. This would give more area for the threads to grab.

Alternatively, tighten the screw down to mark the aluminum, then remove the end stop and drill a 3mm hole just through the track at that spot to engage the screw.

This thing was made with Tinkercad. Edit it online at:
https://www.tinkercad.com/things/fr5LIeKT57b