GM 10 Bolt 8.5" Auburn positive traction differential unit for the 1971 thru 1987 10 bolt 8.5" differnatials with 28 spline axles. Super strong and very durable because it's built right here in the good old USA. Auburn Indiana is the home of these units and they were confident enough of the quality to name them after their town. Always top quality parts at fair prices, give RiversideGear a try!