The ARB Air Locker will fit the following vehicles: > Series I, II, III (1948-1985) - Front Rover Axle and Rear Rover Axle. > Defender 90 (1984-1993) - Front and Rear Diffs [If your vehicle is 1993 pleae check the number of splines]. > Defender 110 (1984-1993) - Front Diff. > Discovery 1 (1989-1993) - Front and Rear Diffs. > Range Rover Classic (up to 1992) - Front and Rear Diffs [when installed to pre-1980 Classic RTC3426 may also be needed]...Created to provide 100% traction on demand, without sacrificing any of your vehicle's highway driving performance, ARB Air Lockers employ a 12 volt air compressor designed to activate (and deactivate) a solid and durable locking mechanism inside the differential. This gives you the traction you need, when you need it, all at the flick of a switch, and all within the safety and comfort of the driver's seat. The advantage of the ARB Air Locker lies in the pneumatically operated locking system inside the differential. When activated, the Air Locker prevents the differential gears from rotating and therefore prevents the axle shafts from turning independently of each other. With both wheels tied directly to the rotation of the crown wheel, the vehicle maintains maximum possible traction at all times. When unlocked, it operates just like a conventional 'open' differential. In addition to providing outright improvements to a 4x4's off road capabilities, the Air Locker offers significant environmental benefits. An Air Locker equipped vehicle can be driven in a slower, safer and more controlled manner, greatly reducing the likelihood of vehicle damage and environmental impact.