Air Locker Locking Differential, Rear 11.5in, All Ratios, Shaft Spline 30 (RD139) by ARB. Created to provide 100 percent traction on demand, without sacrificing any of your vehicles highway driving performance, ARB Air Lockers employ a 12 volt ARB 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 flip of a switch and all within the comfort of the drivers seat.