NGK standard plugs are constructed for longer life and optimum performance. Trivalent metal plating provides superior anti-corrosion and anti-seizing properties. Corrugated ribs prevent flashover. Pure alumina silicate ceramic insulator, provides superior strength and better heat transfer. Copper core aids in heat removal. Triple seals prevent leakage. Thread Size: 12mm. Seat Type: Gasket. Resistor Value: 5K Ohm. Reach: 26. 5mm (1. 04"). Hex Size: 5/8" (16mm). Terminal Type: Solid. Gap: . 035" (0. 9mm).