Mercury - NGK ITR4A-15 Laser Iridium Spark Plug MerCruiser V6 & V8 Series Iridium & Copper Core 8M0204739. Overview. There's nothing quite like that first turn of the key when the engine fires instantly - clean, sharp, and confident. It sets the tone for the entire day on the water. Whether you're easing away from the dock or opening up the throttle across open chop, knowing your ignition system is rock-solid gives you peace of mind that's hard to beat. This Mercury Marine part is built for that