Denso's Iridium power racing spark plugs offer the ultimate in design features. This is because they will not only provide more horsepower, but they are extremely durable even under severe racing conditions. At the heart of these plugs is the world's smallest center electrode, it is only 0.4mm in diameter. This is possible because while Iridium conducts electricity better than platinum, it is also 6x harder and 8x stronger than platinum. This ultra-fine iridium center electrode provides superior ignition performance by more efficiently using the ignition voltage to create a stronger, larger, flash front or spark. Thus you obtain more efficient burning of the air/fuel mixture and more horsepower. Because of the strength and hardness of the iridium center electrode and the fine wire(0.8mm) platinum ground electrode, these plugs are almost impervious to wear even under extreme driving or racing conditions. This makes these plugs not only the best money can buy, but also cost effective as they will far outlast several plug changes of any other plug, even on racing applications. For many non-racing applications, they may out live your vehicle, providing superior performance the whole time. A patented Denso insulator tip design, and a beveled housing, aid in self-cleaning to prevent plug fouling and bridging (carbon build-up between the center and ground electrode). The built-in monolithic resistor body offers the most reliable "talk-back" to electronic ignition systems. Nickel plated for high corrosion resistance and eliminating thread seizing. Each plug is individually packaged in its own plastic case to securely protect electrodes during shipping.