RTS OE Speedometer Gear, 20 Tooth, For Ford Automatic C4 C5 C6 FMX AOD, Will Fit T5 Tremec TKO Magnum, Driven Gear, 3.25, Each - RTS-SPEDO-12Part Number: RTS SPEDO 12 This new speedometer driven gear fits C4 C5 C6 C10 FMX AOD transmissions. Will work with 3. 25 OEM number: C1DZ 17271 A Based on 25. 4" tall tyre Will also fit T5 Tremec T45 T56 Magnum and TKO manual transmission Tech Tip: If you can determine whether your speedometer is reading too slow or too fast, it is worth noting that a lower # of teeth will cause it to turn faster versus a higher # of teeth to turn slower