| 摘要 |
A spark plug capable of increasing a welding strength between a leading end of a metal shell and a base end of a ground electrode to avoid fracture of a welded part due to vibrations and the like even when making the metal shell smaller. The spark plug satisfies a relation of S2≧S wherein S2 is a sectional area of the welded part between the metal shell and the ground electrode, the sectional area S2 being cut off by a plane including a leading end surface of the metal shell, and S is a sectional area of the ground electrode, the sectional area S being cut off by a plane passing to the most axial leading end of a boundary between the ground electrode and the welded part and perpendicular to the axial direction.
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