Sold as a set of 4.  Iridium IX Spark plugs are the most technologically advanced high performance plugs available. Featuring a 0.6 mm iridium center electrode tip, they offer superior ignitability without sacrificing duality. The tapered ground electrode increases flame kernel expansion, while the superior heat range design is ideally suited to the demands of the high performance environments. Specially designed to meet the needs of serious enthusiasts, Iridium IX Spark Plugs offer outstanding acceleration, high fuel efficiency, and long life. When you demand the most from your engine, rely on the proven performance of NGK Iridium IX Spark Plugs. Iridium IX Spark Plugs are the most technologically advanced high performance plugs available. Iridium plugs burn clean and a cooler range of plug can be used without the normally associated risk of plug fouling. This is why we recommend them over the Autolites for the boosted Ecotec.  Choose stock heat range for cars with stock pulleys down to 3.2". Choose one range colder for 3.0" pulley use.  Choose two ranges colder for 2.8" and below pulley sizes.  .033 gap LSJ Iridium plugs have a very delicate tip, make sure you use a proper gapping tool (one that doesn't apply pressure to the tip) to change the gap or you could break off the tip.