Stock Plug for Jr's or Sr's NGK traditional plugs are constructed for longer life and optimum performance. Corrugated ribs prevent flashover. NGK uses only the purest alumina silicate in its ceramic insulator which give all NGK plugs greater strength and better heat transfer. Copper cored and triple sealed to further aid in heat removal and prevent interior leakage. Compact plug for reduced clearance installation. "Flashover" Flashover is when the voltage sent to the spark plug does not fire between the center and ground electrodes within the combustion chamber, instead, it shorts between the metal shell and the terminal nut on the plug exterior causing the engine to misfire. This can occur when the air is highly ionized (such as on a stormy day), or when the insulator is dirty. To reduce flashover NGK has ribbed corrugations on the top portions of the insulator.