These casters are designed to be used as replacements for drywall dollies and sheetrock dollies. The listing is for a set of 4 swivel casters. These caster wheel features a crowned thermoplastic rubber tread the offers maximum floor protection, is non-making, and provides a smooth and quiet roll. Each wheel measures 8 inches in diameter and has a 2 inch wide tread. The mounting height is 9-1/2 inches. The capacity is 600 pounds per caster and 2,400 pounds for all four casters.