| 摘要 |
PROBLEM TO BE SOLVED: To provide a spark plug for an internal combustion engine capable of surely fixing a central electrode whether it is of a large under-brim diameter or a space of a part corresponding to an over-brim part or the like of a through-hole of an insulating body is diminished due to miniaturization. SOLUTION: The spark plug 100 for an internal combustion engine is provided with a main fitting 5, an insulating body 1 having a through-hole 11 in an axis direction, a terminal electrode 3 fixed toward a rear side of the through-hole and a central electrode 2 fixed toward a front side, of which, a minimum distance (L1) between an outer periphery face of an over-brim part 21 of the central electrode 2 and an inner periphery face of the through-hole 11 of the insulating body 1 is not more than 0.7 mm and cross section area of the over-brim part 21 in the direction across the axis is tapered from the front side toward the rear side. As a spark plug with the minimum distance of not more than 0.7 mm, one with the ratio of the maximum diameter of an under-brim part and that at a diameter-changed part of not less than 0.5 and less than 0.8, that is, one with a larger maximum diameter of the under- brim part than usual or the like is cited. COPYRIGHT: (C)2003,JPO
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