A management torque value smaller than a specified torque value is defined beforehand, and a screw ring-form, plug management gauge (11), which is capable of being screwed with plug (3), is prepared. Gauge (11) is provided with marked lines (14a, 14b) showing upper and lower limit positions of tolerance of the orientation of ground electrode (33) when plug (3) and gauge (11) have been screwed with each other. When plug (3) and gauge (11) have been screwed with each other and tightened at the management torque value, suitability of the phase position in the rotational direction is evaluated and managed by whether or not ground electrode (33) of plug (3) is in a range of marked lines (14a, 14b) showing the upper and lower limit positions of the tolerance. With this, it becomes possible to conduct a phase management with consideration of the crushing deformation characteristics of the gasket even with a torque lower than the specified tightening torque.
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