A pulley is a circular object, usually fabricated from heavy duty materials, which is used in numerous applications, the most common of which include applying forces or transmitting force, carrying things or guiding belts, chain, and ropes. The pulley wheel features an axle that is commonly installed to a frame or brace that allows the wheel to spin freely. This reduces rubbing when a rope, chain, or belt runs around the pulley. The outer side of the pulley can be grooved to help guide the belts, ropes, chains or cables preventing them from sliding off the pulley during operation.

The applications of a pulley wheel can differ significantly, and the size of the wheel will often vary based on the function for which it is being used. A pulley wheel can be used in an automotive engine compartment to support the timing belt or the serpentine belt and the pulley may also be used to power peripheral equipment such as power steering machines and air conditioners. These pulleys will be fairly small. By comparison, an exceptionally large pulley wheel may be used on a ski lift at a ski area. This large pulley wheel will help guide the cable on which the chairs are secured and it will help keep proper tension on the cable connection.

Manufacturing facilities and production facilities frequently make use of pulley wheels as part of a process to support lift or move large items. A rope or cable can be strung through one or more pulleys and one end of the cable can be affixed to the object that needs to be moved. Adding pulleys to the process will reduce the amount of energy needed to lift the object, though this could also add friction to the process, therefore making motion more difficult. The proper balance of pulleys must be used to effectively lift or move the objects. Many of these pulley systems are motorized to support move items quicker and to carry extremely heavy objects.

The materials accustomed to create a pulley wheel may differ based on the application for which the wheel will be used. For light duty systems, a nylon or plastic pulley may be enough, though for heavier duty applications, a harder more durable material will be necessary. Pulleys used by automotive engines like crankshaft pulley, timing belt pulleys and underdrive pulleys are typically fabricated from heat resistant precious metals that will not wear out quickly or easily during constant being exposed to high temperatures and regular use.