Magnetic Pulleys are permanent ceramic, but there are instances, where having to alternate conveying material that is magnetic, but should not be separated, requires an electromagnetic pulley. These are also available. Pulleys are available in diameters of 4″, 6″, 8″, 10", 12″, 14", 15″, 16″, 18″, 20", 24", 30", 36 ...Web