Revolution Gear & Axle, replacement series, rear axle shaft for GM 12 bolt truck 73-81 1500 4WD, fits both left and right side, 31.43" 30 Spline (OE 14071750/ Hollander 447-1063). 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% increase over the OEM Axles.