Motive Gear F888390 8.8" Rear Ring and Pinion for Ford (3.90 Ratio) 8620 Steel Performance Differential Ring And Pinion Ratio: 3.90 Pinion Spline: 30 Ring Diameter: 8.8 Pinion Diameter: 1.626 Ring Gear Teeth: 39 Pinion Teeth: 10 Position: Rear