I saw this on the rusty's site when i was looking at the part to their version of the Superlift kit. I knotice this roller on the rear diff. I have never seen this before. It looks like those roller on a boar trailer that help the boat roll on. I assumed it is meant here for protection of the rear diff/driveline u-joint if you were high centered on a rock or cliff. OR some kind of counter balance weight or something.

Does anyone know what this is?