Patent ID: 6373173
Filing Date: 2002-04-16
Classification: H01T

Abstract:
A spark plug comprising:an elongate center electrode; an insulator enclosing the center electrode; a metallic shell having open opposite ends and enclosing the insulator, the metallic shell having a male-threaded portion formed on a front-side outer circumferential surface of the metallic shell, and a tool engagement portion formed on the outer circumferential surface of the metallic shell at a rear side with respect to the male-threaded portion, the tool engagement portion projecting circumferentially outwardly; and a ground electrode connected to the metallic shell and defining a spark discharge gap in cooperation with the center electrode, wherein the insulator has a stepped annular insulator-side engagement portion for engaging with an annular shell-side engagement portion projected inwardly from a portion of an inner surface of the metallic shell corresponding to the male-threaded portion, and |Aâˆ’E|&lE;1.5 mm, and 0.4&lE;(D2/E)2&lE;0.6, where A is a dimension of the tool engagement portion represented by a diameter of an inscribed circle of a cross-sectional outline of the tool engagement portion, E is an effective diameter of the male-threaded portion, and D2 is an inner diameter of an intermediate-bore portion of the metallic shell located on a rear side with respect to the shell-side engagement portion.