Ford Racing ring and pinion sets are engineered, manufactured, and tested for maximum performance. These ring and pinion sets are finished in a black oxide coating for corrosion resistance, and are available in many different ratios to fit a variety of Ford differentials. ** Note: 3.15 Ratio Differential not compatible with 3/31, 3.55, 3.73 and 4.09 ratio gears. Use differential M-4204-MT or M-4204-M. * This part is designed and intended for competition use only. It should not be installed on a vehicle that is driven on public roads and highways. Installation of this art on a vehicle driven on public roads and highways is likely to violate U.S. and Canadian laws and regulations relating to motor vehicle emissions.