Dead simple replacement of the feeble nylon/ptfe spacers that are way too small to stabilize the wheels properly on the Tronxy X1 printer (at least). These are much better at making sure the axes are perpendicular and consequently, to fight wobble that a lot of people experience when assembling their printer.

They are mostly useful for the hot end carrier (you need 3 pieces), and the bed. For the latter I would recommend my bed tensioner though: https://www.thingiverse.com/thing:2854082. They are probably less useful for the arm junction to the Z axis, because these wheels are fully secured on both sides, contrary to the others.