| 摘要 |
In a spark plug having a generally cylindrically shaped metallic body, a generally cylindrically shaped insulator held in the metallic body, a center electrode held in the insulator, and a ground electrode facing the center electrode, the insulator has a ramp portion on an outside surface thereof and the metallic body has a supporting portion for supporting the ramp portion of the insulator. Further, a conductive layer (a protection layer) is formed on the surface of the insulator to face the supporting portion of the metallic body. Accordingly, a corona discharge in a clearance between the supporting portion of the metallic body and the insulator is prevented, so that spike-like noise can be prevented.
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