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-and 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-six times harder than platinum. This allowed NGK engineers to reduce the voltage requirement for a spark. Shorty Spark Plug: No. Resistor: Yes. Manufacturer Heat Range: 5. Electrode Tip Material: Iridium. Electrode Core Material: Copper. Insulator Type: Projected. Spark Plug Thread Size: 18mm. Spark Plug Reach: 0.460 in. Spark Plug Seat Style: Tapered. Wrench Diameter: 13/16 in. Ground Strap Quantity: One.