Revolution Gear and Axle, Replacement series, Rear axle shaft for GM 12 Bolt Car 68-72 Chevelle and El Camino, 70-72 Camaro, fits both Left and Right side, 30.12 Inch 30 Spline (OE# 3969285). Revolution replacement series axles are made from 1541H Steel and utilize a state of the art computer controlled heat treated process. The use of better material and better heat treating process gives our replacement axles a 10 Percent increase over the OEM axles.