Abstract: A safety cap is adapted to assume a locked position on the neck of a container at which an annular cap rib rides within the concavity provided by an annular neck recess. In order to remove the cap, it must first be pulled outwardly to break this interengagement. Thereafter, the cap need only be rotated or turned to free the cap from neck threads. In order to mount the cap on the container neck, the cap is initially twisted to cause interengagement of the threads of the cap with the threads of the container neck. The threads are so arranged that when the cap rib engages the upper part of the neck recess, the last turn will force the rib into the recess and at the same time clear the threads from one another. In this position the cap will turn freely relative to the neck with the cap rib disposed within the neck recess.