Abstract: A readily insertable and removable closure plug comprising an expander core aving a sealing member positioned circumferentially thereon. The expander core comprises at least two adjacent segments, one cylindrical in cross-section and the other tapered in cross-section. The sealing member is annular in shape and has tapered internal and external surfaces. In the uninstalled state, the sealing member is positioned circumferentially about the expander core tapered segment. Flanges on the expander core and sealing member insure proper positioning of the plug. Installation of the plug is effected by forcing the plug into an opening of a container until the container walls contact the sealing member. Continued application of force on the expander core forces the core through the sealing member until the position of the sealing member is changed from circumscribing the expander core tapered segment to circumscribing the core cylindrical segment.