If you're talking about what looks like a pulley on the bottom of the arm it's probably for bending pipe/rods cleanly. Get perfect curves instead of hard 90° bends that might cause issue......and the beveled circle on the bottom of the movable jaw.
Thanks, that picture helps. I have no use for it, but maybe see if the guy will do a deal.the bolt locks the handlw for cranking the die. picture