NGK (4709) FR9BI-11 Iridium IX Spark Plug, Pack of 1 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 Iridium alloy has extremely high melting point, giving it high durability to heat and electrical wear, perfect for today's high-performance engines Trivalent metal plating has superior anti-corrosion and anti-seizing properties