Another mechanism that has a very wide usage in machine design is the slider-crank mechanism. It is mainly used to convert rotary motion to a reciprocating motion or vice versa. Below a she slider-crank mechanism is shown and the parameters that are used to define the angles and the link lengths are given. As in the four-bar mechanism, the extended and folded dead centre positions are when the crank and the coupler are collinear (coupler link is commonly called connecting rod in slider-crank mechanisms). Full rotation of the crank is possible if the eccentricity, c, is less than the difference between the connecting rod and the crank lengths and the crank length is less than the connecting rod length (e.g. ca2)