NGK 7401 UR4IX Iridium IX Spark Plug, Pack of 4 Designed specifically for the performance enthusiast, Iridium IX offers extreme ignitability, improved throttle response and superior anti fouling The 0.6mm laser welded fine Iridium tip ensures high durability and a consistently stable spark and the tapered ground electrode minimizes electrical Quenching Effect Longer insulator nose prevents fouling, the corrugated ribs on insulator prevents flashover, and a triple gasket seal eliminates combustion gas leakage Longer insulator nose prevents fouling, the corrugated ribs on insulator prevents flashover, and a triple gasket seal eliminates combustion gas leakage Iridium alloy has extremely high melting point, giving it high durability to heat and electrical wear, perfect for today's high-performance engines