Denso platinum spark plugs provide superior resistance to erosion and corrosion, enabling extended operation. Taper cut, U-Groove ground electrode design gives the flame a groove to grow in, resulting in less flame dissipation and a larger flame front for a more complete combustion. This translates to better fuel efficiency and improved throttle response. 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.