Patent ID: 7086363

Claim:
A spark plug comprising: a mounting bracket to be mounted to an internal combustion engine; a center electrode having both a base extending so as to be exposed from an end of the mounting bracket in an axial direction of the plug and a tip end part secured to a distal end of the base in a line in the axial direction, the base being insulatedly-supported by the mounting bracket and formed to taper toward the tip end part and the tip end part having, a cylindrical form; and an earth electrode coupled with the one end of the mounting bracket and is formed to have a cylindrical protrusion extending toward the center electrode so as to face the tip end part of the center electrode in the axial direction, a spacing serving as a discharge gap being formed between the tip end part of the center electrode and the protrusion of the earth electrode, both of the tip end part of the center electrode and the protrusion of the earth electrode being 2.3 mm or less in diameter, respectively, and the discharge gap being 0.7 mm or less in length.