Abstract: Screw on caps for bottles that have an anti back off feature formed on a hinged tab of the cap engaging detent teeth below the threads on the bottle. The hinge has a unique configuration that enables the tab to snap into and hold a gripping position while avoiding temporary distortion or creep. The detent teeth are particularly suited for use with blow molded bottles and are capable of restraining a cap within a small angle of a fully tightened position to avoid any significant back off and potential leakage. In one embodiment, the anti back off feature is provided in a child resistant cap while in another embodiment this feature is provided in a simpler continuous thread cap.