Speedmaster™ copper core spark plugs feature a cold-formed steel shell with precision-rolled threads, a full copper core electrode to provide better performance, triple-ground electrode for more efficient combustion and a one-piece terminal post to add strength. Speedmaster™ copper core spark plugs use a copper-glass seal that bonds the insulator and terminal post center electrode together. This ensures full voltage at the spark gap and a 100 percent leak-proof, gas-tight seal. Keep your engine running smoothly and reliably with Speedmaster™ copper core spark plugs.