This is the Level 2 600HP Complete Axle for the 1989-1997 Thunderbird and 1999 Mustang Cobra (28 Spline Differential). The outer CV is a proprietary material with a unique Carbo Ausse Tempering that gives it a very hard shell and it fits the stock wheel hub. These axles also feature our chromoly 108 mm Porsche-type Ball & Cage inner CV with a bolt-on flange and spline plug to fit the 28 spline differential and our high grade aircraft quality center bars.