Mercury - Quicksilver Cotter Pin Propeller Hardware Stainless Steel 47959. Overview. It's a tiny piece, but without it, your prop wouldn't stay put. The Mercury Marine 47959 Quicksilver Cotter Pin is one of those small, often overlooked parts that plays a huge role in keeping your setup safe and solid. It locks your prop nut in place so your propeller doesn't loosen or back off while you're running. Made from marine-grade stainless steel, this cotter pin stands up to torque, vibration, and saltw