Denso Iridium Power spark plugs feature a 0.4mm iridium tipped laser welded fine wire center electrode that reduces required voltage and improves firing performance. Tapered cut U-Groove ground electrode increases ignitability and decreases quenching. 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.