Abstract: A closure for a container having an opening includes a base cap and an overcap that form a chamber adjacent the opening which is sealed from the contents of the container by a frangible membrane having an inclined line of weakness and by a hinge member having a pocket extending downward adjacent lower and upper terminuses of the line of weakness. The overcap includes a cutting member received within the pocket that severs the line of weakness upon substantial rotation of the overcap with respect to the base cap. A pushing member may cooperate with a cam member to deflect open the membrane upon severance. The pocket may include a stop for the cutting member. The base cap may include a cylindrical structure having an upwardly inwardly projection member to form a seal with an thickened upper portion of the overcap skirt to protect against penetration into the chamber.

Abstract: There is described a neck structure in combination with a closure. The neck structure defines a neck opening with a cylindrical sealing surface surrounding the neck opening and an external neck surface. The closure comprises a cap formed of resilient material having a top and a downwardly extending skirt portion depending from the top. An annular plug depends from an underside of the top and one or more ribs are formed on an internal surface of the downwardly extending skirt portion. The annular plug and the one or more ribs are arranged concentrically and are dimensioned such that, upon application of the cap to the neck structure, the annular plug projects into the neck opening and engages the cylindrical sealing surface. At the same time the one or more ribs engage the external neck surface.