Original Name / Part No.: 8579Part location: Inside rear gearboxProduct major functions & usage:Improve the transmission of power in the differential caseAccessories:Ring Gear 1pcPinion Gear 1pcStainless Steel Flat Head Screw 2.5x8 4pcsMajor advantages of upgrading to this part/product:1. The material is upgraded to harden steel #45 to make it more durable and sturdy to use.2. Reduce the gap in between gears, in order for the gears to run smoother and more powerful.