Dana 60 Chrome-Moly Full Steel Spool - 35 Spline - 4.56 & Up - D60 35 Spline 4130 Heat-Treated Moly Material - Extra Strong Maximum Strength & Reduced Rotating Weight Fits 4.56 & Numerically Higher Gear Ratios (4.56, 4.88, 5.13 etc) Provides Complete Lockup of Rearend