Mugen MBX8R HTD High Traction Front/Rear Differential Set. Package includes the parts needed to build one complete replacement differential with 42 tooth ring gear, that can be used in the front or rear position. High traction Differentials (HTD) are used to provide increased acceleration, longer runtimes and more consistent handling. A larger volume differential cup increases consistency allows the racer to easily time rhythm sections and further increase traction.