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Claim 1

A CLOSURE SEAL FOR A CAP TYPE CLOSURE ADAPTED FOR USE ON A CONTAINER HAVING A SEAL ENGAGING SURFACE ON THE UPPERMOST EXTREMITY THEREOF COMPRISING A PLASTIC DISC INCLUDING A RELATIVELY THIN CIRCULAR CENTRAL PORTION, A RELATIVELY THICK INNER CONCENTRIC SEALING RIB, A RELATIVELY THIN FLEXIBLE ANNULAR FLEX-RING PORTION EXTENDING BEYOND SAID INNER SEALING RIB, SAID SEALING RIB AND SAID ANNULAR FLEX-RING PORTION ENCIRCLING SAID CENTRAL PORTION, THE SEALING RIB BEING OF SUCH A DIAMETER THAT IT WILL BEAR APPROXIMATELY AGAINST THE UPPERMOST PORTION OF THE LIP OF THE CONTAINER TO BE SEALED, AN OUTER MARGINAL RIM ENCIRCLING SAID FLEXRING PORTION OF GREATER THICKNESS WITH RESPECT TO THE RADIALLY INNER SEALING RIB, AND SUBSTANTIALLY FLAT UPPER AND LOWER SURFACES ON SAID OUTER MARGINAL RIM COOPERATING WITH SAID GREATER THICKNESS WHEREBY SAID CLOSURE SEALS WILL CRACK STACK VERTICALLY WITH LIKE CLOSURE SEALS AND SLIDE THEREOVER WITHOUT INTERLOCKING, SAID ANNULAR FLEX-RING PORTION HAVING SUFFICIENT WIDTH BETWEEN SAID OUTER MARGINAL RIM AND SAID CONCENTRIC SEALING RIB TO ALLOW A SUBSTANTIAL DEGREE OF FLEXURE OF SAID MARGINAL RIM RELATIVELY TO SAID SEALING RIB AND TO LOCATE SAID SEALING RIB IN POSITION TO ENGAGE THE UPPERMOST PORTION OF THE LIP OF THE CONTAINER TO BE SEALED.