| 摘要 |
A spark plug includes: a metal shell defining a front side having an outer periphery formed with a screw section which has a nominal size smaller than or equal to M12; a center electrode; a conductive seal layer; a terminal metal fitting fixed to the center electrode via the conductive seal layer; and an insulator formed with a through hole. The terminal metal fitting has a Vickers hardness in a range from 150-300 Hv. The terminal metal fitting includes: a front end section having an outer diameter, and embedded in the conductive seal layer, and a small diameter section disposed on a rear side of the front end section and having an outer diameter which is smaller than the outer diameter of the front end section. The through hole has an inner diameter different from the outer diameter of the small diameter section in a range from 1.0-1.4 mm.
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