| CPC B65D 41/145 (2013.01) [B65D 41/045 (2013.01)] | 18 Claims |

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1. An apparatus, comprising:
a cap liner comprising:
an outer lip, wherein a cross-section of the outer lip comprises a single upper extension member and a single lower extension member;
an inner portion surrounded by the outer lip and comprising a substantially uniform thickness; and
a protuberant outer nub projecting radially outward from the outer lip and defining an outer perimeter of the cap liner,
wherein the cap liner is symmetric about a symmetry plane centered within the substantially uniform thickness of the inner portion,
wherein a maximum thickness of the protuberant outer nub in a direction perpendicular to the symmetry plane is less than the substantially uniform thickness of the inner portion, and
wherein a cross-section of the protuberant outer nub has a convex outer surface that is rounded outward,
wherein the outer lip comprises a substantially flat outer edge extending between top and bottom surfaces of the outer lip,
wherein the protuberant outer nub projects radially outward from the substantially flat outer edge and is substantially centered between the between top and bottom surfaces of the outer lip without extending to the top and bottom surfaces of the outer lip.
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