Features: Standard plug-in type twin wheel casters. Application: For replacing casters on office chairs. Caution: *Please check the dimensions before purchasing, as they may not be compatible with all office chairs. *Standard nylon casters are best suited for carpeted floors, while urethane casters, which are less likely to scratch, are recommended for hard floors such as flooring, tile, and concrete. *When replacing the casters on an office chair, be careful as they may be very difficult to pull out. Wheel Diameter (Φmm): 50 Shaft Diameter (Φmm): 11 Shaft Length (mm): 22 Type: Swivel Color: Black Material (Wheel): Urethane rubber Wheel Width (mm): 51.8 With no stopper Caster Type: Plug-in casters Wheel Type: Twin wheel Set of 4 black casters, smooth movement I accidentally purchased these. They are unused.