| 摘要 |
In a first embodiment a spark plug satisfying the relations: t>=0.3 mm and St/Sw<=7 in which t is the axial-direction shortest distance between a leading end surface 41 a of a precious metal tip 41 and a joint portion 43 , St is the surface area of the precious metal tip 41 and a joint portion 43 between the precious metal tip 41 and the ground electrode body 4 a, and Sw is the area of the joint portion 43 between the ground electrode body 4 a and the precious metal tip 41 . In a second embodiment, the spark plug satisfies the relations t>=0.3 mm and La>Lb; and in a third embodiment the spark plug satisfies the relations t>T and La>Lb, where T, La and Lb are as defined in the specification. The relation t>=0.3 mm is specific to the first and second embodiments, and the relation St/Sw<=7 is specific to the first embodiment only.
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