HKS Super Fire Racing Iridium Spark-plugs are designed to offer outstanding performance on both stock and tuned engines.HKS have engineered these spark plugs with outstanding designed to stand up to the demands of highly tuned engines.HKS Super Fire Racing Spark Plugs use a 0.6mm Iridium Alloy Center Electrode. This is standard on performance spark plugs. It improves durability and ignition performance and requires a lower voltage to make a spark.The outer electrode features a platinum chip which boosts ignition performance whilst improving durability. It's also been designed to be short for improved resistance against vibration.The plugs outer casing is designed to resist carbon build-up to help prevent misfires.The reduced voltage requirements of the plug help ensure the ignition performance even under high boost pressure.For rotary applications, HKS use a different design of plug with an electrode design engineered specifically for the unique requirements of these engines.Please not