Air cylinder for easy height adjustment. Five 2.5" casters for ease of mobility. Cushioned black vinyl cover. Large, reinforced 15.25" diameter 1" deep tool tray. Individual replacement casters available Sunex seats are sure to keep you mobile and comfortable while doing any job. This professional seat works in any shop environment. The seat is 12.5" in diameter. It's made with the quality and durability to last!