For when using 1.5" Square Tube (1/8" wall) in projects such as the LowRider v3 CNC, this end cap protects against snags and scrapes (v1.0). Prints with no supports. PLA. Can be scaled a bit as needed in your slicer to get a tight fit. Mine fits tight just as it is. Also, a bit of painters tape around the stub can help tighten a loose fit. Enjoy!
PS: photos show some of my build progress on a CNC plasma cutting table based on LowRider v3 platform.