Round Tread Polyurethane on Aluminum Core - PM. Composed of a polyurethane elastomer, open cast or injection molded, on clean, close tolerance cores. Wheels feature a chemical and mechanical lock of tread to the core. High capacity polyurethane protects floors, is non-marking and delivers quieter operation than standard metal wheels. Hardness: 90 Shore A (green) or 80 Shore A (butterscotch). Wheels are complete with top hat and spacers. Wheel face: Round tread. Finish: Green tread on aluminum core. Temperature Range: -40 degrees to +180 degrees Fahrenheit.