Cast iron is one of the strongest hubs available and moldon wheels are solid rubber with little or no tread which makes this wheel ideal for the heaviest loads. These have the highest load capacity at around 900 pounds. This wheel is a Rolling Ball B earing. Does not come with Zerk or Grease Fitting.These wheels are best suited for smooth warehouse floors where they can roll easily. Available in six options. For moving the heaviest loads over smooth surfaces order these high capacity wheels today . Wheel Weight Diameter Tread Width Hub Length Axel Bore Weight Capacity 5" 2" 2.1875" .75" 3.25 lbs. 500 6" 2" 2.1875" .625" 4.25 lbs. 500 6" 2" 2.1875" .75" 4.25 lbs. 500 8" 2" 2.1875" .625" 6.25 lbs. 600 8" 2" 2.1875" .75" 6.25 lbs. 600 10" 2.5" 2.75" 1.00" 13.75 lbs. 800NOTE: Weight Capacity is per Whee