| 摘要 |
A spark plug is disclosed as including a metal shell 10 formed with first and second bores 10 c, 10 d and a stepped section 10 e between the first and second bores, and a porcelain insulator 20 having a largest-diameter section 20 d, which is accommodated in the first bore and a small-diameter section 20 e accommodated in the second bore. The first and second bores of the metal shell have a dimensional relationship, lying in a value equal to or less than 1.8 mm, which is expressed as (D 1 -D 2 )/2 where D 1 represents an inner diameter of the first bore of the metal shell and D 2 represents an inner diameter of the second bore of the metal shell.
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