Is this a picture of a DIY project? Could be anything, but yeah a round rubber or polyurethane, that can rotate, or a static low friction teflon/etc bumper wheel.
It wouldn't need to be done like that. You could make an end-cap/guide/whatever out of teflon, or another low abrasive material... can't see the other end, which would presumably need something similar.
You could even put another end cap there, and a little lube on the contact area.
Last edited by Dave9; 07/12/19 06:32 PM.