| 摘要 |
<p>A spark plug (1) has an outer tube member (11) that covers the outer peripheral surface of the projecting part (2a) of an insulator (2) beyond a main metallic shell (3), with its front end being coupled to the main metallic shell (3). A hexagonal tool engaging portion (13) is formed in the rear end portion of the outer tube member (11). No tool engaging hexagonal portion is formed in the main metallic shell (3). Accordingly, even if a plug hole (PH) of a smaller diameter is formed, the outside diameter of the insulator (2) need not be reduced accordingly since the heretofore required hexagonal portion is eliminated. As a result, the mechanical strength and withstand voltage of the insulator (2) can be ensured at adequately high levels. <IMAGE></p> |
