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 350lbs/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 400lbs/ea with a thread width of 2", and a overall height of 6-1/2". The 6" casters has a load capacity of 450lbs/ea with a thread width of 2", and a overall height of 7-1/2". The 8" casters has a load capacity of 500lbs/ea with a thread width of 2", and a overall height of 9-1/8".