Duralast ® - the protective wheel that wears like steel - is liquid cast to a thickness of approximately 1/2" and chemically bonded onto heavy-duty iron wheel centers. The distinctive green treads are chemically inert, non-sparking, non-conductive, impervious to ozone, grease and most oils & solvents, and will not mark floors. Duralast® Wheels are also guaranteed against tread separation for one year in ordinary free-wheeling applications (contact factory for excepted applications).