Patent ID: 8058785

Claim:
A spark plug comprising: a metallic shell having a shell bore extending axially therethrough and a first open end proximate a spark gap; an insulator being at least partially disposed within the shell bore, the insulator having an insulator bore extending axially therethrough and a first open end proximate the spark gap, the insulator having an intermediate portion adjoining an end portion, the end portion having an exterior surface that abuts an interior surface of the first open end of the metallic shell and the end portion has a nose portion axially extending beyond the first open end of the metallic shell by a first length, the end portion defining a counterbore that extends inwardly into the insulator from the first open end of the insulator; and a center electrode at least partially disposed within the insulator bore and having a first end forming part of the spark gap, the center electrode extending beyond the first open end of the metallic shell by at least the first length, wherein a portion of the center electrode is located within the counterbore and an air insulation gap extends from the portion of the center electrode received within the counterbore to an inner surface of the end portion defining the counterbore, wherein the insulator further comprises a projection extending axially within the counterbore, the projection being located within the counterbore and wherein the projection is located about a portion of the center electrode located within the counterbore and wherein the air insulation gap is located between the inner surface of the counterbore and an exterior surface of the projection.