Slide the socket onto equipment legs and tighten the thumb screw. Wheels have a hard polypropylene core for strength under a polyurethane tread that combines the abrasion resistance of plastic with the shock-absorbing qualities of rubber. They can be used on smooth and rough floors and in areas with debris. Ball bearings in the wheel provide easy rolling. Casters have dual-raceway swivel bearings for the smoothest swiveling.