Closure means

Claim 1

IN COMBINATION WITH A CONTAINER HAVING A CIRCULAR OPENING IN THE UPPER END THEREOF SURROUNDED BY A SHOULDER AND AN INWARDLY AND DOWNWARDLY EXTENDING LIP, SAID LIP HAVING A SUBSTANTIALLY CYLINDRICAL INNER EDGE SURFACE, A CAP FOR SAID OPENING COMPRISING A LID PORTION NORMALLY ENGAGING SAID SHOULDER AND AN INTEGRAL, TUBULAR PLUG PORTION EXTENDING INTO AND THROUGH SAID OPENING, SAID PLUG PORTION HAVING A FIRST FLANGE ADJACENT TO THE LOWER END THEREOF WHICH IS OF GREATER OUTER DIAMETER THAN THE INNER DIAMETER OF SAID LIP AND IS NORMALLY POSITIONED BELOW SAID LIP WITH ITS UPPER SURFACE ENGAGING SAID LIP, SAID PLUG PORTION HAVING A NECK PORTION ABOVE SAID FIRST FLANGE AND HAVING AT LEAST ONE OUTWARDLY EXTENDING SEALING TONGUE NORMALLY ENGAGING SAID SUBSTANTIALLY CYLINDRICAL SURFACE OF SAID LIP, SAID PLUG PORTION HAVING A SECOND FLANGE ABOVE SAID NECK PORTION OF GREATER OUTER DIAMETER THAN THE INNER DIAMETER OF SAID LIP AND NORMALLY POSITIONED ABOVE THE INNER EDGE OF SAID LIP, SAID PLUG PORTION HAVING AN ANNULAR RECESS BETWEEN SAID SECOND FLANGE AND SAID LID PORTION WHICH EXTENDS INWARDLY FARTHER THAN SAID NECK PORTION AND DEFINES A FRANGIBLE PORTION BETWEEN SAID LID PORTION AND SAID PLUG PORTION, AT LEAST ONE OF SAID CONTAINER AND SAID CAP BEING ELASTIC AND THE VERTICAL DISTANCE BETWEEN THE UPPER SURFACE OF SAID FIRST FLANGE AND THE LOWER SURFACE OF SAID LID PORTION IN UNSTRESSED CONDITION BEING LESS THAN THE VERTICAL DISTANCE BETWEEN SAID SHOULDER AND THE LOWER EDGE OF SAID LIP WHEREBY SAID LID PORTION NORMALLY IS HELD TIGHTLY ENGAGED WITH SAID SHOULDER AND SAID LOWER EDGE OF SAID LIP IS HELD TIGHTLY ENGAGED WITH THE UPPER SURFACE OF SAID FIRST FLANGE.