| 摘要 |
PROBLEM TO BE SOLVED: To provide a spark plug in which sufficient airtightness and stability of tightening state can be achieved in a main body fitting and an insulator and which can respond to demand of small diameter. SOLUTION: The spark plug 1 includes the insulator 2 having an axial hole 4 penetrating in an axis line C1 direction, a center electrode 5 inserted in the axial hole 4, a main body fitting 3 installed at the outer circumference of the insulator 2, and a grounding electrode 27 which is installed on the main body fitting 3 and forms a spark discharge gap 33 between the tip part of the center electrode 5. The main body fitting 3 has a rear end side opening part caulked to form a caulking part 20, and is combined to the insulator 2 with the caulking part 20 locking with the rear end portion of a large-diameter part 11. Here, an annular groove portion 23 is provided at least at the portion to be opposed to the inner end fringe of the caulking part 20 out of the insulator 2. Thereby, an engaging margin of the caulking part 20 can be secured sufficiently. COPYRIGHT: (C)2009,JPO&INPIT
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