Inside Diameter: The distance across the center hole, or bore, of the product. This dimension should match the diameter of your shaft or bolt.
Material: Describes what the product is made from. Plastic, aluminum, and diecast are softer, lighter, and do not rust. Steel and cast iron are meant for heavy-duty applications, but can rust in certain circumstances.
Outside Diameter: The distance across the circle of the product, from outside edge to outside edge.
Width: The distance from side to side of the pulley, across the area where the belt rides