Swivel 6 caster with 6 x 2 RollXWow wheel.
"Swivel 6 caster, 6 x 2 Phenolic wheel, total lock"
Swivel 6 caster with 6 x 2 Ductile Iron (crowned) wheel
Swivel 6 caster with 6 x 2 Mold-on rubber wheel
