A pulley is a basic mechanism for lifting large items. It is made up of a wheel with a grooved track through which the rope, chain, or belt may pass. As the name suggests, there are several types of pulleys available, depending on the application. A single-speed pulley uses one groove to lift one weight; a double-speed pulley uses two pairs of oppositely facing grooves to lift twice as much weight; and a triple-speed pulley uses three pairs of oppositely facing grooves to lift three times as much weight. In addition, there are also combination pulleys that combine features from different types of pulleys to produce even more efficient lifts. The type of pulley used depends on the application. For example, if you were to build a pulley system for your home garage, you would want to use a single-speed pulley because that will allow you to lift a maximum amount of weight with no risk of breaking something. If you were to build a commercial garage pulley system, we recommend using a double-speed pulley so that if someone decides to lift a heavy item by hand instead of using a machine, they won't be able to put all their weight behind it and cause the garage door to open!