| 摘要 |
<P>PROBLEM TO BE SOLVED: To prevent corrosion or the like of an insulator and maintain sufficiently bonding strength of a grounding electrode to a body metal fitting and moreover to surely prevent breakage or the like of the grounding electrode. Ž<P>SOLUTION: The spark plug 1 is provided with a central electrode 5, an insulator 2 holding the central electrode 5 with its top end projecting in a direction of an axial line CL1 from its own top end surface, the body metal fitting 3 having threaded part 15 where threads are formed and having a cylindrical part 42 as well where no threads are formed on its outer circumferential face in a region from the threaded part 15 at least to the top end of the insulator 2 along the axial line CL1 direction, and a grounding electrode 27 with its own base end jointed with a top end part 3a of the body metal fitting 3. On the cylindrical part 42, there is formed a groove part 51 made of a bottom face 52 located nearer the side of the base end than a top end 2a of the insulator 2 and two sidewalls 53, 54 formed in continuation with the bottom face 52 and the top end face 3a of the body metal fitting 3. The base end of the grounding electrode 27 is jointed to the bottom face 52 of the groove part 51. Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž
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