The Dynarex DynaRide S1 S2 S3 Reclining Wheelchair Hub Cap (Dynarex Item # RPWC9-K123) is the factory-original protective center dust cover for the rear wheels. Molded in durable black plastic, this cap snaps directly into the center of the 24-inch mag wheel hub to shield the internal wheel bearings and axle assembly from moisture, dirt, and external debris