Impreza WRX/2.5 RS (GC8/GD) 500HP Rear Axles (R160 Differential ONLY). The 500HP axles use our new proprietary outer CV that is a direct fit to the factory wheel hub, our aerospace grade torsional 32 spline axle bars, increased from the factory 29 spline bars, and a billet ball & cage inner cv with our high grade inner differential spline for the R160 differential.