This type of caster features gray non-marking injection molded rubber that is mechanically and chemically bonded to the hub. They are especially suited for use in Pharmaceutical Laboratories, Hospitals, Food Service and other Institutional applications. The wheels provide a softer ride than polyurethane and yet withstand exposure to many chemicals and solvents. The top mounting plate for this caster is 2.78” by 2.33”. The bolt pattern, which is the distance between each installed bolt, is 2.15” by 1.64”. The diameter of each bolt hole is 0.35”. When this caster is installed, it adds an additional 3.70” of overall height to the item you are attaching it to.