Abstract: An adhesive is applied to a male-threaded portion of a tapping screw. The male-threaded portion with the adhesive is threadably engaged with a non-threaded through hole of the full-closed stopper with female-threads being formed on the surface of the though hole. In this case, the adhesive functions as lubricant between the inner surface of the through hole and the male-threaded portion. Accordingly, the male-threaded portion can be screwed into the through hole with a low torque and without applying high load to the full-close stopper. Therefore, the full-close stopper is prevented from being projected around the inlet and the outlet of the through hole, and the full-close stopper is prevented from being cracked.