A closure combination of a closure plug for shipping containers and a tamper evident, closure overseal, the closure plug (6, 45) and the overseal (20, 52) having hidden, complimentary, interlocking, snap-fit features (17, 49, 23, 56, 24, 57) and a frangible portion (26, 53a), to permit removal of the overseal from the plug, that is visible when the closure plug and the overseal are interlocked; the interlocking, snap-fit features may be internal or external of the closure plug but are hidden by the overseal skirt (22, 54) and the overseal is destroyed on removal from the closure cap.