| 摘要 |
PROBLEM TO BE SOLVED: To provide a spark plug which is superior in anti-fouling property while a channeling is hard to occur and which has a good durability and also a good ignitability. SOLUTION: The spark plug 100 has an insulator 1 that is equipped with a center through hole, a center electrode 2 that is retained by the center through hole and that is made to protrude a tip face of the insulator 1, a main metal fittings 5 which retains the tip part of the insulator 1 so that the tip part protrudes from own tip face, and a semi creepage ground electrode arranged so that one end is joined at the main metal fittings 5 and the other end is opposing to a side circumferential face of the center electrode 2 or opposing to a side circumferential face of the insulator 1. Then, in case a step difference between the altitude position of the tip face 1D of the insulator 1 and the altitude position of the rear end side border of the end face 12C of semi creepage ground electrode is assumed as E, and a radius of curvature of curved surface reaching side circumferential face from the tip face 1D of the insulator 1 is assumed as R, R-E<=0.1 mm is satisfied.
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