| 摘要 |
A spark plug having a protrusion amount t of not smaller than 0.3 mm and satisfying a relation theta 1+theta2 <=93° in which theta 1 is an included angle between virtual lines s 1 and s 2 , and theta 2 is an included angle between virtual lines s 3 and s 4 when the virtual line s 1 is taken as a line parallel to a direction of an axis and including the other end side edge on a leading end surface of a first precious metal tip, the virtual line s 2 is taken as a line connecting the other end side edge and a point of intersection between an inner circumferential surface of a ground electrode body and the other end surface of the ground electrode body, the virtual line s 3 is taken as a line parallel to the direction of the axis and including the other end side edge on a leading end surface of a center electrode, and the virtual line s 4 is taken as a line including the other end side edge and tangent to an insulator.
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