NGK 3521 Spark Plug Designed specifically for the performance enthusiast, Iridium IX offers extreme ignitability, improved throttle response and superior anti-fouling The 0.6 millimeter 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 provides superior anti-corrosion and anti-seizing properties; Part number of spark plug inside the box: CR9EIX