Multi-Ground Electrodes Improve Ignition Capabilities and are Less Sensitive to Increased Voltage Requirements Due to Gap Growth.. Designed to Specific Manufacturer Ignition Requirements, NGK's Multi-Ground Plugs Maintain All the Features of Their Standard Plugs, Including:. Corrugated Ribs to Prevent Flashover Pure Alumina Silicate Ceramic Insulator, Providing Superior Strength and Better Heat Transfer Copper Core to Aid in Heat Removal Triple Seals to Prevent Leakage Thread Size: 12mm Thread Pitch: 1.25mm Seat Type: Gasket Resistor Value: 5K Ohm Reach: 26.5mm (1.04") Hex Size: 5/8" (16mm) Terminal Type: Solid Overall Height: ISO Gap:.035" (0.9mm)