A spark plug is a device for delivering electric current from an ignition system to the combustion chamber of a spark-ignition engine to ignite the compressed fuel/air mixture by an electric spark. The plug has a metal threaded shell, electrically isolated from a central electrode by a porcelain insulator. Spark plugs are specified by size, either thread or nut, sealing type and spark gap. Watch the video below and find out how spark plugs are made!

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