The patented ARB Dana 30 Air Locker 27 Spline 3.73 and Up is built to withstand the worst of conditions. Constructed from aerospace-grade high-alloy steel, the materials in the piece are good enough for spaceships -- and they'll work for your vehicle. The overall design enhances long-term durability by reducing the number of moving parts while still evenly distributing torque loads. A number of designs also have patented timed gear sets that improve total strength.