Revolution Gear and Axle, Replacement series, Rear axle shaft for Ford 9.75 Inch 99-04 Expedition and F150 w/1.705Bearing, Left Hand, 33.5 Inch 34 Spline (OE# F75Z4234LB and YL1Z4234CB). 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.