To provide a plug which prevents shortcomings such that the pitches are not favorably engaged with each other due to a breakage or deformation of the pitch, the adhesion of foreign object or the like at the pipe end of a water supply pipe or the like which is opened/closed by the pitch, or since the material of the plug itself mainly is the same plastic as the water supply pipe or the like, the plug is weak against impact from the outside, and the material causes a breakage or deformation of the plug itself; and also, when another plug is substituted for the plug because of the breakage or the deformation or the like of the plug, the plug and the water supply pipe or the like are not favorably engaged even if the difference in the size or the shape of the pitch is very small, and the plug cannot be used.

For the material of this plug, rubber which is excellent in shrinking property, sealability and impact-resistance as well, is used. Also, an already existing pitch on the pipe end of the water supply pipe is utilized, and pitch is not applied on the internal side of the plug. Therefore, the plug can be used for the pipe end regardless of the size or the shape of the pitch of the pipe.