| 摘要 |
PROBLEM TO BE SOLVED: To provide a long-life, high-performance spark plug for an internal combustion engine. SOLUTION: A center electrode 2 and a grounding electrode 3 are both made using a nickel alloy as a base material and is jointed noble-metal chips 12, 13 to the discharge parts of their respective ends. The noble-metal chip 12 of the center electrode is made of iridium or an iridium alloy and inserted into a hole 20 axially bored in the end of the center electrode. When the outside diameter of the noble-metal chip 12 is A, the outside diameter of the end 21 of the center electrode 2 is B, and the amount by which the noble-metal chip 12 is projected from the center electrode is C, B-A>=0.8×C is preferable within the range of 0.6<=A<=1.2mm and 0.4mm<=C<=1.0mm. When the axial length of the noble-metal chip 12 is E and the distance from the end of the noble-metal chip to the end of an insulator is D, a relation of E>=D should preferably be met.
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