This is genuine Dana/Spicer posi trac or limited slip differential additive. You add this to the gear oil of your choice to help lubricate the clutches in the differential. One 4 ounce bottle will do most differentials, although we do recommend two bottles for differential with more capacity, such as a Dana 80. This is Made In The U.S.A. Shipping is FAST and FREE in the continental U.S.