Mercury - Forward Gear Pinion 12/21 - 8M0146648 - Fits engines listed below: 200 HP 4.6L V8 Pro XS - Serial number 2B529482 and Above 225 HP 4.6L V8 Pro XS - Serial number 2B529482 and Above 225 HP 4.6L V8 SeaPro - Serial number 2B529482 and Above 250 HP 4.6L V8 - Serial number 2B529482 and Above 250 HP 4.6L V8 Pro XS - Serial number 2B529482 and Above 250 HP 4.6L V8 SeaPro - Serial number 2B529482 and Above 250 HP 4.6L V8 Verado- Serial number 2B529482 and Above 250R HP 4.6L V8 Racing- Serial number 1E080500 and Above 300 HP 4.6L V8 - Serial number 2B529482 and Above 300 HP 4.6L V8 Pro XS - Serial number 2B529482 and Above 300 HP 4.6L V8 SeaPro - Serial number 2B529482 and Above 300 HP 4.6L V8 Verado- Serial number 2B529482 and Above 300 HP 4.6L V8 Verado SeaPro- Serial number 2B529482 and Above 300R HP 4.6L V8 Racing- Serial number 1E080500 and Above