Mercury - Reverse Gear 12/21 for Counter Rotating 5.44 Torpedo Lower Unit- See Below for Applicable Engines - 8M0146676 200 HP 4.6L V8 Pro XS - 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 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 Verado - Serial number range 2B529482 and Above 300 HP 4.6L V8 Verado SeaPro - Serial number range 2B529482 and Above 300R HP 4.6L V8 Racing - Serial number range 1E080500 and Above