The caster is a wheel located at the equipment bottom to transport the equipment smoothly. It is available in a flexible type and a fixed type. In carrying a heavy load, it is generally said that the load can easily be moved with a small force by using movable rear wheels. Movable front wheels provides more operability, but is not suitable for a heavy load. The wheel material is rubber, polyamide (nylon), phenol, engineering plastics, or stainless steel. Flange type or screw type caster fittings are available.