Spark plugs have been around as long as internal combustion engines. Spark plugs are a "window" into the engine, and can be a valuable diagnostic tool. The spark plug displays the condition inside the combustion chambers of the engine. The experienced tuner can use spark plugs to find the root cause of problems, determine air-fuel ratios, and to increase vehicle performance. Since 1936 NGK has lead the industry in technology, innovation and world class design of its entire product line. You can depend on NGK for quality and reliability. Types, Styles, and Hex Sizes vary by model.