A gear so called because it is usually located between a driving gear and a driven gear, transmitting the power from one to the other. It also transmits the direction of rotation of the driving to the driven gear. Without the idler or the intermediate gear, the driving gear by directly meshing with the driven gear reverses the direction of rotation. Idler wheels or pulleys are also fined for tightening belts or chains or to maintain a uniform tension on them.
