A main body that has an installation portion which is formed from an elastic material having a cylinder shape, and installed at the metal opening at one end side a lid insertion portion which cylindrically protrudes to the other end side, and a lid connected to the main body by a flexible connection portion having flexibility, that is formed from an elastic material, that has a tube shape with a cylindrical insertion channel, and that, at both sides where both ends of the insertion channel are respectively open, has first and second installation portions with different external shapes to each other which are installed by selectively inserting to the lid insertion portion. The first installation portion has a larger external shape than the second installation portion, at least a portion of a diameter of the insertion channel decreases when installed to the lid insertion portion of the first installation portion.
