Air Locker locking differentials allow you to tackle the toughest terrain. As the world's premier traction aid, ARB Air Lockers keep you moving in all conditions. While developing the Air Locker for the 2012 T6 Ranger and Mazda BT50, ARB Engineers noted the similarities between the differential dimensions with the Landrover Discovery Series 3. With the only difference being the ring gear diameter, this resulted in development of the RD217. This Air Locker fits the front axle of the Land Rover Discovery 3 and 4.