These casters are made of polyurethane on cast iron and come in four different sizes: 4", 5", 6", and 8". The casters are designed to be rigid, swivel, and brake. The total lock feature ensures that the casters are locked in both the swivel and wheel rotation directions. The casters are colored in green and have a load capacity of 670lbs/ea for 4" casters, with a thread width of 2", and a overall height of 5-5/8". The 5" casters has a load capacity of 800lbs/ea with a thread width of 2", and a overall height of 6-1/2". The 6" casters has a load capacity of 900lbs/ea with a thread width of 2", and a overall height of 7-1/2". The 8" casters has a load capacity of 950lbs/ea with a thread width of 2", and a overall height of 9-1/8".