Polyurethane tread with plastic core. Size: 4" diameter, 1-1/4"(1.25") width, 3/8"(0.375") bore. Quiet operation, Dual precision bearing, much heavier load capacity than other marketing products: up to 300lbs each. Fits Mutiple enviroment, Lowest Highest Temperature:-40F to +180F, resistant oil, acids, grease and water.Durable Non-marking and floor protective, Fits most of shopping cart, grocery carts, moving dollies, office &store fixture, hotel, food and warehouse equipment.