RWM Cast Iron wheels are made of much stronger material than inexpensive semi-steel wheels offered by many other wheel manufacturers. These cast iron wheels can withstand high temperatures and exposure to water or the environment. They will rust over time. Cast iron wheels can also withstand exposure to chemicals, grease, oils, etc. All wheels 1-1/2" and wider with roller bearings are equipped with a metal thrust/retainer washer. All wheels 2" wide are generally lubricated through the hollow axle. Lubrication fittings can be installed on the hub upon request on most of these wheels. RWM cast iron wheels are exceptionally long wearing, provide excellent resistance to shock and are a good choice for heavy loads in manufacturing and warehousing, especially on rough concrete, wood block and other rough surface conditions. 4", 5", 6" and 8" diameter, 2" wheels are solid hub.