| 摘要 |
PROBLEM TO BE SOLVED: To prevent breakage of an insulator by improving strength of the insulator.SOLUTION: A spark plug is equipped with the insulator 2 and the main metal fitting 3. The insulator 2 has a large diameter part 11, a contracted diameter part 15, and the rear-end side trunk part 10, and the main metal fitting 3 has a tool engaging part 20, a caulking part 21, and a seat part 17. The caulking part 21 is locked to the large diameter part 11 via a ring member 24 and talc 26. In the spark plug in which the outer diameter of the rear-end trunk part 10 is 7.0 mm or more and 8.0 mm or less, opposite side size of the tool engaging part 20 is 12 mm or less, or the outer diameter of the rear-end side trunk part 10 is 9.0 mm or more and 10.5 mm or less. The distance from the seat part 17 along an axial line CL1 to the rear end of the insulator 2 is 42 mm or more and 54 mm or less, 1/2 of diameter difference between the outer diameter of the rear-end side trunk part 10 and the inner diameter of the ring member 24 is 0.15 mm or more, and the diameter of the ring member 24 in a cross-sectional face to include the axial line CL1 is 0.4 mm or more. |
