ARC offer 2 styles of wheels. The black wheel on the left is manufactured from high impact acetal material. This wheel runs on 2 x 3/8" bore high speed bearings with an anti-crush sleeve between them. For the budget minded, the grey wheel on the right is manufactured from high impact plastic, with a vulcanized rubber contact surface. This wheel has an acetal sleeve running full width which runs on a 1/2" chrome moly shaft/crush sleeve. Neither wheel gives any problem in service.