Denso Iridium Tough spark plugs feature a 0.4mm iridium tipped laser welded fine wire center electrode and platinum tipped ground electrode. Burnished nickel plating for high corrosion resistance. 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.