USA Standard Gear standard spider gear set for Ford 8. 8", 31 spline, open differential.Material:Steel 7/8" cross pin shaft. 31 Spline application. Does not work on 28 Spline applications. Does not work on positraction/limited slip differentials. 1985 & older 31 spline applications have a 3/4" cross pin shaft and require a new carrier case. Technical Note 1: There were both 28 and 31 spline factory options available for over lapping years. Please check your spline count before ordering. Technical Note 2: There were limited slip and standard open carriers available for these applications, where ordering this part for the incorrect case would create fitment issues. Please open your differential cover and confirm the factory carrier in your vehicle. Technical Note 3: Aftermarket 31 spline carrier cases and upgraded 31 spline axle shafts are available for many of the stock 28 spline applications. Again, we strongly urge you to first open up your differential and count the splines on your carrier to ensure proper fitment.