Autolite 86 Copper Core Spark Plug, Pack of 1 Mixture of nickel and copper-glass seal that bonds the insulator, terminal post and center electrode together, assuring full voltage Chromium-nickel alloy ground electrode resists gap erosion Copper-core center electrode sheathed in high chromium-nickel alloy for superior heat dissipation and durability Longer insulator nose provides a longer path to control fouling deposits