| 摘要 |
PROBLEM TO BE SOLVED: To secure a withstand voltage appropriately in a spark plug of thin size having a mounting screw part of M10 or less. SOLUTION: The mounting fitting 10 is provided with a mounting screw part 11 of M10 or less at the outer circumference. The portion having the maximum diameter in the circumference direction out of the portion located inside the mounting fitting 10 of the insulating insulator 20 is formed as a barrel 22, and the portion adjoining the barrel 22 on one end 20a side of the insulating insulator 20 is formed as an intermediate step part 23 having a smaller diameter than the barrel part 22. The barrel 22 and the intermediate step part 23 of the insulating insulator 20 are opposed to the inner face of the mounting fitting 10 through a gap. When the inner circumference diameter of the portion opposed to the barrel 22 via a gap out of the mounting fitting 10 is made D1 and the inner circumference diameter of the portion opposed to the intermediate step part 23 via a gap is made D2, (D1-D2)/2 is made 1.8 mm or less. COPYRIGHT: (C)2005,JPO&NCIPI
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