Heavy duty "Dyna-Tred" swivel caster. 4 in. diameter. Steel plate, without total lock braking system. Metal protective thread guards (standard on Dyna-Tred blue wheel). Two full independent rows of hardened, polished precision ball bearings roll freely in large-diameter, lubricated raceways. Fully seated wheel roller bearings eliminate the need for lubricating axle and reduces maintenance costs. Corrosion-resistant zinc finish. Load capacity: 300 lb. Sold by the unit.