Abstract: The disclosure concerns a screw cap comprised of semi-rigid plastic material and including a tamper-proof hold ring. The screw cap is for use on the neck of a container, such as a bottle. The hold ring has an inside diameter that is at least equal to the outside diameter of the cap body. Six lock lugs supported on the ring are inclined upwardly and inwardly toward the neck closing end of the cap body. The lock-lugs elastically hook behind a collar or mating ring at the bottle neck to prevent the tamper-proof hold ring from being lifted off the neck of the bottle when the cap body is unscrewed. Breakable attachment tabs initially hold the cap body to the tamper-proof hold ring and these are broken as the cap is initially unscrewed. An unbreakable flange between the cap body and the tamper-proof ring serves as a tilt hinge for the unscrewed cap.

Abstract: A one piece screw type bottle cap, a method of applying it and a method of molding it. The cap includes an internal sealing skirt having a cylindrical portion that seals against the internal surface of the bottle neck. The skirt flares inwardly and terminates at an outwardly extending collar which is bent upwardly before applying the cap to the bottle neck, and which engages the neck to form an additional seal only after the threads of the cap interengage with the threads of the neck.

Abstract: A screw-type bottle cap molded in one piece from plastic material comprises an internal sealing skirt depending from the top of said cap and adapted to be force-fitted into the externally threaded neck of a bottle, a first sealing lip concentric with said skirt and positioned to engage the upper end of the neck of said bottle when said cap has been screwed home, and a second sealing lip adapted to cooperate with the upper outer surface of said bottle neck. The sealing skirt comprises a short upper portion having a slight outward conicity when unstressed, and the external diameter of which, at its connection to the top of said cap, is greater than the maximum internal diameter of said neck, allowing for manufacturing tolerances. Said upper portion merges into a central portion having an inward conicity, and terminating in a substantially radial collar, the periphery of which is adapted to bend upwardly as the cap is screwed down to form an additional seal with the inner surface of said bottle neck.