NGK's standard plugs are constructed for longer life and optimum performance. Tivalent metal plating provides superior anti-corrosion and anti-seizing properties. Corrugated ribs prevent flash-over. Pure alumina silicate ceramic insulator provides strength and better heat transfer, while copper core aids in heat removal. Triple seals prevent leakage. Center and ground electrodes are constructed from nickel. 12mm thread size. 1.25mm thread pitch.