Platinum’s superior resistance to erosion and corrosion enables Denso double platinum spark plugs an extended operation in excess of 60,000 miles. Platinum tipped ground and center electrodes. Machine rolled threads prevent seizing or cross threading during installation and removal. 100% pre-fired to assure the highest quality possible. Purified alumina powder insulator provides exceptional strength and thermal conductivity. Five rib insulator prevents flashover. Copper-glass seal bonds center electrode and insulator for a gas-tight seal.