This medium-duty swivel caster has a cast iron 1 1/2 x 5-inch wheel with a silver core. Each caster has a load rating of 500 pounds and a double ball swivel raceway type. The mounting plate is 4 1/8 x 3 3/8 inches, with a mounting bolt diameter of 5/16 inches and an inside/outside bolt hole spacing of 2 3/8 x 3 1/8 inches. The frame is made from zinc with a zinc finish. Use the item number WCS515B 5/8 for replacement wheels.