Bosch (7979) HR9DCX+ Super Plus Spark Plug, (Pack of 1) Heavy-duty yttrium-enhanced copper core center electrode for superior reliability and increased resistance to spark erosion for a 50% longer performance life vs. even OE plugs Tapered, v-profile nickel chromium ground electrodes improves cold start performance and increases fuel ignitability Angular, five-ribbed insulator design prevents misfire due to current leakage Nickel-plated rolled threads provides complete anti-seize and corrosion protection Metal glass fused resistor maximizes interference suppression