The Stewart Warner Speedometer Gear Ratio Adapter Series 666F is a vintage part designed for adjusting speedometers for different rear end ratios.  I used this on a TH400 changing from 2.73 to 4.56 gears. Made in the United States by Stewart Warner, this adapter is a performance part that allows users to adjust the gear ratio of their speedometer for increased accuracy. With a 0.500 ratio, this adapter is ideal for car enthusiasts looking to enhance the performance of their vehicle's interior gauge system.