Denso (DK20PR-D13) Iridium Spark Plug 100 percent Pre-Fired: All Denso spark plugs are 100 percent pre-fired to assure the highest quality possible; Solid terminal nut Copper-Glass Seal: Bonds the center electrode and insulator together for a gas-tight seal; Maintains proper heat and excludes hot combustion gases Purified Alumina Powder Insulator: Provides exceptional dielectric strength and thermal conductivity allowing the material to stand up to extreme stress Platinum-alloy tipped fine wire ground electrode, with a platinum pad on the ground electrode and an Iridium pad with cross grooves on the center electrode DENSO (3476) DK20PR-D13 Iridium Spark Plug, Pack of 1