This RDJ7J spark plug is supplied by the original manufacturer for use in outdoor power engines. It is a small, cylindrical component that creates the spark responsible for igniting the air and fuel mixture in the engine combustion chamber. It has a ceramic insulator, a metal rod, known as the center electrode, and a metal tab at its base...Read more, known as the ground electrode. Over time, the spark plug can become fouled with carbon deposits or wear out, leading to decreased engine performance, misfires, and reduced fuel efficiency. You can find the spark plug in the engine cylinder head. Use a multimeter or spark tester to confirm that the spark plug is no longer functioning. Disconnect the spark plug wire and use a spark plug socket wrench to unthread the faulty spark plug. Use a gaping tool to set the correct gap size on the new spark plug and thread it into the engine cylinder head by hand, before tightening it with the wrench