| 摘要 |
PROBLEM TO BE SOLVED: To provide a spark plug used for a high-powered engine for racing or the like, enabled to effectively prevent or restrain beake of a ground electrode. SOLUTION: When the length of welded section W in the extending direction L is regarded as w, and the length of the part extending from the welded section W to a spark gap g side is regarded as d, a ground electrode 4 fulfills either one of the conditions stated below. (1) d/d+w is adjusted to 0.5-0.58, and the area of the axial cross section of the straight columnar body forming an electrode protrusion part is 0.64-2 mm<2> . (2) d/d+w is adjusted to 0.5-0.7, and the area of the axial cross section of the straight columnar body forming an electrode protrusion part is 0.8-2 mm<2> .
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