Spark plug for an internal combustion engine

摘要

In a spark plug, a cylindrical metal shell is provided whose inner wall has a ledge portion on which an insulator rests through its seat portion. The insulator has an axial bore in which a center electrode is placed whose front end has a heat-resistant metal tip. A ground electrode is provided to form a spark gap with the noble metal tip of the center electrode. The insulator forms an insulator nose which measures less than 15 mm in length. The heat-resistant metal tip measures less than 0.8 mm in diameter. A space between an outer surface of the center electrode and an inner wall of a front open end of the axial bore is defined to be more than 0.1 mm in width.