Mold-on Rubber/Cast Iron (Wheel Dia range: from 4" to 18") Semi-soft black Rubber on black painted Cast Iron core. This wheel offers a semi-cushioned ride, rolls over debris and on uneven surfaces well and offers decent floor protection, however the tread is soft black rubber that can mark. These wheels are fairly inexpensive and are very popular on trash containers, platform trucks, lumber carts and countless other applications. These wheels perform well on lighter applications but don't handle overloading very well. If overloaded above the recommended weight capacities; the rubber tread can split and crack, These wheels typically come with a zerk fitting on the hub that allows the bearings to be lubricated without removing the wheel from the caster or equipment. Hubs are usually spoked. Typical sizes are 4 x 1-1/2 up to 16 x4 and 18 x 3. Durometer: 75 to 85 Shore A. Temperature Range: -40 to +160 Degrees / F.