This is a modification of the stock foot for a Voron Zero with a recess for a half inch (13mm) 3M Bumpon. I didn't like the bolt on rubber feet that are stock with the V0, I much prefer the softer white rubber bumpons from 3M. The benefit of this design is that a shorter screw can be used to mount the feet of the printer, it also has registration nubs to prevent it from coming out of alignment with the frame.