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.
