Indexed spark plugs align the open end of the electrode toward the intake port. The hottest flame meets the new fuel charge for a performance gain, increases fuel mileage and plug life. This is a speed secret car racers have used for years. You simply mark the electrode side of the plug with a magic marker on the porcelain. You then shim the plugs with the washers to align the electrodes toward the intake ports. Fits 14mm threaded spark plugs. Indexed spark plugs align the open end of the electrode toward the intake port The hottest flame meets the new fuel charge for a performance gain, increases fuel mileage and plug life This is a speed secret car racers have used for years You simply mark the electrode side of the plug with a magic marker on the porcelain You then shim the plugs with the washers to align the electrodes toward the intake ports Note: Fits 14mm threaded spark plugs
