DENSO's standard spark plug is something special. The innovative U-Groove design that helped to make DENSO spark plugs famous, employs a unique, channeled ground electrode designed to generate a larger spark at the point of ignition. Greater spark energy than ordinary plugs means improved flame travel, producing more complete, consistent, and efficient combustion.The innovative U-Groove design that helped to make DENSO spark plugs famous, employs a unique, channeled ground electrode designed to generate a larger spark at the point of ignition.Greater spark energy than ordinary plugs means improved flame travel, producing more complete, consistent, and efficient combustion.