| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a spark plug capable of securing anti-loosening property of a main metal fitting that is fixed by screwing in a mounting hole with a sealing member interposed. <P>SOLUTION: The spark plug 1 is dismounted from an engine head 90, and an equivalent friction diameter D1 is obtained on the basis of the outer diameter d1<SB POS="POST">o</SB>and the inner diameter d1<SB POS="POST">h</SB>of a contact mark J remaining on the overhang portion 54 of a main metal fitting 50 subjected to Ni plating, the mark formed by contact with a gasket 60 made of a stainless steel. Similarly, an equivalent friction diameter D2 is obtained on the basis of the outer diameter d2<SB POS="POST">o</SB>and the inner diameter d2<SB POS="POST">h</SB>of a contact mark K remaining on the opening edge 92 of a mounting hole 91, the mark formed by contact with the gasket 60. The plug satisfies D1<D2. The plug also satisfies Dz>D2, when the largest outer diameter of a surface facing the gasket 60 is defined as Dz, in the overhang portion 54. <P>COPYRIGHT: (C)2012,JPO&INPIT |
