9" Ford Chrome-Moly Full Steel Spool - 35 Spline Provides Complete Lockup of Rearend 4130 Heat-Treated Moly Material - Extra Strong Scalloped Design Provides Maximum Strength & Reduced Rotating Weight Fits 3.25" Aftermarket Cases Drag Racing, Off-Road, Demolition Derby, Truck Pulling, Mud Bogging, Circle Track