Patent ID: 7109646

Claim:
A spark plug comprising: a main metal fitting having a cylindrical structure; an insulator disposed inside the cylindrical main metal fitting and having an inner hollow structure; a center electrode fitted in the inner hollow portion of the insulator in a manner that a front end portion of the center electrode projects outward over one end of the insulator; and a grounding electrode mounted to the main metal fitting and having one end portion opposing to the front end portion of the center electrode with a discharge gap therebetween, wherein said front end portion of the center electrode includes a conical portion having a tapered surface and a columnar portion formed to a top end portion of the conical portion, said columnar portion having a diameter in a range of 0.4 mm to 0.8 mm and said tapered surface of the conical portion having a taper angle of less than 80°, and wherein said columnar portion has an axial length in a range of 0.3 mm to 1.0 mm.