Standard Open Spider Gear KitFord 8.8" Open DifferentialWith 31-Spline Axles 0.875" cross pin shaft diameterCompatible with the following Differentials: Ford 8.8" - 28 Spline Ford 8.8" - 31 Spline Ford 8.8", '10 & up Mustang & '10 F150 only - 31 spline Ford 8.8", '11 & up F150 only - 31 spline.