Patent ID: 7528534

Claim:
A spark plug comprising a tubular insulator having an axial through hole and a first insulator stepped portion that reduces an outer diameter of the tubular insulator toward a front end side of the tubular insulator, a rod-shaped center electrode disposed in the through hole of the insulator, a metallic shell having a first metallic shell stepped portion that reduces an inner diameter of the metallic shell toward a front end side of the metallic shell and supporting the insulator through engagement of the first metallic shell stepped portion and the first insulator stepped portion by interposing therebetween a packing, and a ground electrode connected at one end to a front end surface of the metallic shell and facing the other end portion of the ground electrode toward the center electrode for thereby forming a spark discharge gap between said other end portion and the rod-shaped center electrode, characterized in that: the tubular insulator and the metallic shell, when observed in a section made by a plane including the axis of the spark plug, have therebetween a gap of less than 0.45 mm at a more front end side of the tubular insulator than an engagement position of the packing and the first insulator stepped portion; and the gap between the tubular insulator and the metallic shell is provided axially from a most front end side engagement position of the packing and the first insulator stepped portion as a starting point to a finishing point that is apart from the starting point by 1.2 mm or more toward the front end side of the metallic shell while being apart from the front end surface of the metallic shell by 7.9 mm or more toward a rear end side of the tubular insulator.