Mercury - Forward Gear Pinion 12/21 - 8M0146659 - See Below for Applicable Engines: 175 HP 3.4L V6 - Serial number range 2B529482 and above 200 HP 3.4L V6 - Serial number range 2B529482 and above 200 HP 3.4L V6 SeaPro - Serial number range 2B529482 and above 200 HP 4.6L V8 Pro XS- Serial number range 2B529482 and above 225 HP 3.4L V6 - Serial number range 2B529482 and above 225 HP 4.6L V8 Pro XS- Serial number range 2B529482 and above 225 HP 4.6L V8 SeaPro- Serial number range 2B529482 and above 250 HP 4.6L V8- Serial number range 2B529482 and above 250 HP 4.6L V8 Pro XS- Serial number range 2B529482 and above 250 HP 4.6L V8 SeaPro- Serial number range 2B529482 and above 250 HP 4.6L V8 Verado- Serial number range 2B529482 and above 250R HP 4.6L V8 Racing- Serial number range 1E080500 and above 300 HP 4.6L V8 - Serial number range 2B529482 and above 300 HP 4.6L V8 Pro XS- Serial number range 2B529482 and above 300 HP 4.6L V8 SeaPro - Serial number range 2B529482 and above 300 HP 4.6L V8