A pulley can be fixed or movable. A fixed pulley, such as the one found at the top of a flagpole, is attached to a structure. Fixed pulleys have a mechanical advantage of 1. A movable pulley moves along with the load that is being carried. It has a mechanical advantage of 2. A block and tackle pulley system combines a fixed and movable pulley. This type of system can often be found on cranes. The mechanical advantage of this block and tackle is 4.