US Patent 7528534 Spark plug

There is provided a spark plug wherein an insulator and a metallic shell, when observed in a section made by a plane including an axis of a spark plug, have therebetween a gap of less than 0.45 mm at a more front end side than an engagement position of a packing and a first insulator stepped portion, and the gap is provided axially from a most front end side engagement position of the packing and a 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 while being apart from a front end surface of the metallic shell by 7.9 mm or more toward a rear end side.