| 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 break of a ground electrode. SOLUTION: For the spark plug 1, a ground electrode 4 has an external shape linearly extending in the radial direction against the center axis line O at the orthogonal projection on a first projection plane P perpendicular to the central axis line O of a mounting screw part 6. When a second projection plane Q, parallel either to the central axis line O and the extended direction L of the orthogonal projection figure of the ground electrode 4 on the projection plane P, is considered, a side surface (a first side surface) J of the ground electrode 4 at the side near to a spark gap g has a shape of linearly extending in the direction getting near to the center axis line O, from an end A where the ground electrode is connected to a main metal fitting 5 toward a top end B, at least up to middle section. The whole part of the ground electrode 4 is made of Pt alloy containing 22-40 weight% of Ir.
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