This is a custom t-slot track. It will be used on a crosscut sled for my table saw (will post photos soon). I can print 3' of this for a few dollars vs $30+ for an aluminum track.
The tracks print around 6" and have two tapped screw holes. The slot is designed to be used with an M8 bolt (5/16 should work too). There are two files. One track can be used with just a bolt. The other has a slightly wider slot in which I use an additional washer inside the track.
Uncle Jessy's Gun Metal Silver
I print these with 0% infill but with 4 or 5 walls. This will give it more than enough rigidity. I don't have to clamp or tighten anything too tightly to this track, so PLA will work just fine.