Screw caps

Claim 1

An elastic deformable screw cap for a container having a neck with external threads and having a bore extending through the upper end surface of the neck, the cap comprising: a base portion having an inner surface facing toward said neck; a flexible truncated conical lip extending downwardly from a root portion where it joins said inner surface of the base portion and converging toward a smaller free end of lesser diameter than said bore; an annular abutment comprising multiple concentric ribs extending downwardly from the inner surface of the base portion toward the upper surface of the neck and surrounding said root portion and spaced therefrom, the concentric ribs extending lesser distances than said lip from said inner surface of the base portion and respectively extending to decreasing extents away from the root of the lip; and a skirt portion joining said base portion at its upper end and having internal threads adjacent to its lower end for engaging the threads on said neck, the skirt portion having a cross-sectional portion extending from the base portion to said internal threads along an inner surface which curves smoothly outwardly and downwardly from the outer concentric rib along an inner surface which is a portion of an ellipse and joins said internal threads at a distance below the free end of the lip at least equal to the height of the lip, said curved cross-sectional portion being deformable inwardly toward the neck when the skirt portion is tensioned by screwing the cap tightly on the neck.