How many classes of levers are simple machines?

There are three classes of levers in simple machines. These classes are distinguished by the relative positions of the effort (force applied), the load (resistance), and the fulcrum (pivot point). The first class has the fulcrum between the effort and load, the second has the load between the effort and fulcrum, and the third has the effort between the load and fulcrum. Each class has unique advantages and applications in mechanical advantage.