| 摘要 |
PROBLEM TO BE SOLVED: To prevent damage, or the like, on an insulator more reliably while ensuring excellent airtightness.SOLUTION: A spark plug 1 comprises: an insulator 2 having a reduced diameter portion 14; and a main metal 3 having a protrusion 21 protruding radially inside, and provided on the outer periphery of the insulator 2. The protrusion 21 has a reduced diameter portion 21A, and a locking part 14 is locked to the reduced diameter portion 21A via an annular plate packing 22. In a cross-section including an axial line CL1, following relation is satisfied;θs>θp, where theθp(°) is the acute angle out of the angles formed by a straight line orthogonal to the axial line CL1 and visible outline of the locking part 14, and theθs(°) is the acute angle out of the angles formed by a straight line orthogonal to the axial line CL1 and visible outline of the reduced diameter portion 21A. In the cross-section, following relation is satisfied; Hvo>Hvi, where the Hvo(Hv) is the Vickers hardness of the plate packing 22 at the midpoint CP1 of a first line segment SL1, and the Hvi(Hv) is the Vickers hardness of the plate packing 22 at the midpoint CP2 of a second line segment SL2. |
