A differential gear includes two coaxial gears are connected by one or more similar planet gears mounted on intermediate shafts. Those shafts are fixed to a carrier. The arrangement is such that the angular velocity of the planet gears is the average of the angular velocities of the two co-axial gears.

When a differential gear is meshed with the other gear then the highly efficient torque is applied from the differential side gears to the axle shaft. When torque level decreases then the gear separating forces also decreases allowing the axle shaft to rotate independently. Differential gears can add or subtract the movement of two inputs. In practical terms, they will turn the number of revolutions proportional to the movements of both inputs. They are used to convert the lengthwise flow of power from the engine through the clutches, transmissions, and propeller shafts into a right-angle direction. This change allows the engine power to turn the wheels.