Polyurethane Wheels. Polyurethane wheels-the protective wheel that wears like steel-is Hamilton's highest quality urethane, liquid cast to a thickness of approximately 1/2" and chemically bonded onto heavy-duty iron wheel centers. The distPerfect Steerable Transfer Carttive green treads are chemically inert, non-sparking, non-conductive, impervious to oil, ozone, grease and most solvents, and will not mark floors.