| 摘要 |
The present invention provides a highly reliable spark plug used for an internal-combustion engine and including an insulator with a high withstand voltage, and a method for manufacturing the same. Namely, it provides a spark plug containing a cylindrical metal shell having an insulator holding hole, a cylindrical insulator including an axial hole therein which extends in an axial direction, and engaging with said insulator holding hole of said metal shell, and a center electrode held in said axial hole of said insulator, wherein said insulator has a texture in which one or more pores exposed in a judgment area with 50 mum in diameter occupy 40% or less of said judgment area at any locations in an observation area, in the case where a predetermined mirror-finishing section of an enclosed portion surrounded by said metal shell is used as said observation area to observe pores exposed in said observation.
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