| 摘要 |
PROBLEM TO BE SOLVED: To secure sufficient airtightness while realizing excellent productivity and handling easiness in a spark plug of such a type that a taper face is in contact with a bearing surface when mounted to a combustion device.SOLUTION: A spark plug 1 comprises: an electric insulator 2 extending in an axial line CL1 direction; and a main metal fitting 3 provided on an outer periphery of the electric insulator 2. The main metal fitting 3 comprises: a screw section 15 to be screwed with a mounting hole 42 of an internal combustion engine 41; and a seat section 17 having a taper face 16 whose outside diameter gradually gets smaller toward a tip. When the screw section 15 is screwed with the mounting hole 42, the taper face 16 comes into contact with a bearing surface 43 of the internal combustion engine 41. An annular, or spiral protrusion 16P having length of one or more cycles is formed in a range from at lest an outermost periphery of the taper face 16 to a portion at which it has an outside diameter of 95% outside diameter at the outermost periphery. On a cross section including the axial line CL1, arithmetic average roughness of a surface of the taper face 16 in the range is 1 μm or more and 5 μm or less. |
