Ultra-Fab Products 48-979011 4" Ultra Swivel Skid Wheel Drop forged caster is superior in strength to other casters and extra strong metal wheels with roller bearings and 1/2-inch urethane on luster edge Prevents tail dragging and digging while backing up - helps protect undercarriage from damage Swivel skid wheels 4" low profile RV's up to 30 feet Easy bolt on installation - 2 per box Manufacturers 1-Year Warranty