Mold-on Rubber on Aluminum These wheels have a softer durometer and a higher grade of rubber tread than the RS wheels. Rubber tread is chemically bonded to an aluminum core. The aluminum core is lighter weight, and is stronger than a cast iron core; it is also resistant to many environments that would tend to corrode a cast iron core. Good for applications that require a more cosmetically pleasing look, like retail displays, institutional & food service equipment, etc. Durometer: 70 to 75 Shore A. Temperature Range: -40 to +160 Degrees / F.