This is the Motorcraft XL3 rear axle additive friction modifier used on many Ford applications. For use on applications with limited slip differentials for proper protection for the clutches within the differential. Check your owner's manual and/or the rear axle assembly if needed. Part number is XL-3 with specification number EST-M2C118-A. This is sold by the single 4 ounce bottle. Quantity discount is available.