Mercury - Prop Nut, Rear V12 Contra-Rotating Prop System Brass 8M0176915. Overview. When you run a boat powered by a Mercury V12, you get used to a certain feeling - a steady, confident push that never seems to hesitate, even when the water turns sloppy or the load gets heavy. That confidence doesn't come from the engine alone. It comes from every component working together, right down to the hardware holding your props in place. The Mercury 8M0176915 Rear Prop Nut is one of those pieces you rar