Spark plug with a stepped insulator and an inner constriction in the housing

摘要

A spark plug is disclosed, in which the insulator is formed with a stepped portion near its tip portion and the housing which surrounds the insulator is formed with an inner constriction which opposes the smaller portion of the insulator, near the stepped portion, with a small annular gap being left therebetween, thereby hindering the entry of air/fuel mixture and carbon particles into the inner space between the housing and the insulator, and thus reducing the buildup of carbon on the insulator.