Patent ID: 7825572

Claim:
A spark plug comprising: a center electrode; an insulator having an axial hole extending in an axial direction of said spark plug, said insulator holding the center electrode at a leading end side within the axial hole; and a metal shell having a cylindrical hole extending in the axial direction, said metal shell holding at least a portion of the insulator within the cylindrical hole, wherein the metal shell comprises: a mounting portion having an external thread formed on at least a portion of an outer peripheral surface thereof for engaging an internal thread of a mounting hole of an internal combustion engine; a cylindrical portion formed integrally with the mounting portion at a leading end side thereof and having a smaller diameter than that of the mounting portion; a tapered seal portion connecting outer peripheral surfaces of the cylindrical portion and the mounting portion, the tapered seal portion being spaced apart from the external thread in the axial direction; a crimping portion provided at a rear end of the metal shell, said crimping portion holding the insulator within the cylindrical hole by crimping; and a buckled portion provided between the mounting portion and the crimping portion, and adapted to be deformed in conjunction with the crimping of the crimping portion, and a relationship A<B is satisfied, in which A is a length in the axial direction of the external thread formed on the mounting portion, and B is a length of the cylindrical portion in the axial direction.