Dana 30, Ratio 3.73 and Up (RD104) 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.