Polyurethane on Aluminum Core - PD. Composed of a polyurethane elastomer, open cast or injection molded, on clean, close tolerance cores. Polyurethane tread is chemically bonded to aluminum core. High capacity polyurethane protects floors, is non-marking and delivers quieter operation than standard metal wheels. PA wheels feature cast aluminum core. PD wheels feature die cast aluminum cores. Hardness: PA 95 Shore A, PD 60 Shore D. Finish: Green tread on aluminum core. Temperature Range: -40 degrees to +180 degrees Fahrenheit.