Spark plug

A spark plug comprising a shaft-like insulation member made of ceramic and having a center electrode projecting from a front end thereof, and a metallic shell fixing the insulation member in a surrounding manner and having a ground electrode provided at a front end thereof,

• the insulation member having a front end shaft portion located toward a front end thereof and formed in such a manner as to form an annular insulation space between the front end shaft portion and an inner circumferential surface of the metallic shell, and a mating shaft portion located rearward of the front end shaft portion, having a diameter greater than that of the front end shaft portion, and disposed in a mating hole portion of the metallic shell,
• the insulation member being inserted into the metallic shell from a rear end of the metallic shell, a frontward movement of the insulation member in the course of insertion being checked at a predetermined position by stopper means, and the insulation member being fixed in the metallic shell in a pressed-frontward condition by means of a crimp portion provided at the rear end of the metallic shell being bent toward an axis and pressed frontward,
• characterized in that the stopper means comprises an annular butt portion of the insulation member located rearward of the mating shaft portion, having a diameter greater than that of the mating shaft portion, and assuming the form of a surface facing frontward, and an annular support ledge of the metallic shell located rearward of the mating hole portion, having a diameter greater than that of the mating hole portion, and assuming the form of a surface facing rearward and the butt portion butts directly or indirectly against the support ledge to thereby check frontward movement of the insulation member, and that
• a filler for maintaining gas tightness is provided in a filling manner between an outer circumferential surface of the mating shaft portion and an inner circumferential surface of the mating hole portion.