NGK Iridium IX spark plugs feature an ultra-fine center electrode that's designed just thick enough to ensure the maximum durability and life of the spark plugs?Çöand just thin enough to create an accurate and consistent spark. They represent the ultimate evolution of spark plug technology and performance. Iridium is the hardest metal used in spark plugs today?Çösix times harder than platinum. This allowed NGK engineers to reduce the voltage requirement for a spark. Iridium IX plugs are available in more than a hundred configurations for universal and vehicle-specific applications.