| 摘要 |
In a spark plug 100, the outer diameter of a tool engaging portion 1e formed on a main metal member 1 is not larger than 14 mm. An insulator 2 is provided with a expanded diameter portion (2e) positioned within the main metal member 1 and projecting radially outward from an outer circumferential surface of the insulator, and an intermediate trunk portion (2g) adjacent to an axial front side of the expanded diameter portion (2e) and having a cylindrical outer circumferential surface. The inclined portion (2j) has a linearly inclined outer circumferential surface formed in a position so as to connect the expanded diameter portion (2e) and intermediate trunk portion (2g), and formed so that in orthogonal projections with respect to a plane of projection parallel to an axis O, the diameters become smaller from the side of the expanded diameter portion (2e) toward that of the intermediate trunk portion (2g). In the position in which an extension of the outer circumferential surface of the inclined portion (2j) and that of the outer circumferential surface of the intermediate trunk portion (2g) cross each other, a built-up portion (2k) is formed so that a valley-like space defined by these two extensions is filled.
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