DENSO’s patented U-Groove spark plug enables complete combustion by allowing the spark to fill the gap created by the U shape. The ball of fire created in the U-Groove develops a larger and hotter flash front that virtually eliminates excessive fouling and erratic starts caused by poor fuel mixtures. Even DENSO’s “standard” spark plug is something special. The innovative design that helped to make DENSO spark plugs famous, the U-Groove plug employs a unique, channeled ground electrode designed to generate a larger spark nucleus at the point of ignition. Greater spark energy than ordinary plugs means improved flame travel, producing more complete, consistent, and efficient combustion.