Provided is a screw ring-shaped plug management gauge (11) which may be screwed with a plug (3) and determine a management torque value smaller than a specified torque value. Marked lines (14a, 14b) are disposed at the gauge (11) to show upper and lower limit positions of tolerance toward an outer side electrode (33) when the plug (3) and the gauge (11) are screwed with each other and tightened by the management torque value. Appropriateness of a phase location in a direction of rotation is assessed and managed by discerning whether the marked lines (14a, 14b) for the outer side electrode (33) of the plug (3) to show the upper and lower limit positions of the tolerance are within a range or not when the plug (3) and the gauge (11) are screwed with each other and tightened by the management torque value. Therefore, phase management considering crushing transformation characteristics of a gasket is available even when the torque is lower than the specified tightening torque.
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