Add CASTERS to your hopper for mobility and free your valuable fork truck. Casters are available for hopper sizes through 21 /2 cubic yards—6" or 8" diameter—in a two swivel/two rigid combination. All wheels have roller bearings; swivel casters have hardened double-ball raceway and 3/4" kingpin. Hoppers are shipped with casters bolted to the base; casters may be field installed.