Abstract: A sealing closure for a container, such as bottles, jars and the like includes a threaded cap and a single-piece gasket of resilient material. The interior surface of the top of the threaded cap is provided with a plurality of radially extending ribs in the vicinity of its periphery. The peripheral portion of the single-piece gasket contacts the ribs, the cap being positionable over the rim of the neck of a container and in threaded engagement therewith to seal the container. The gasket may be of frusto-conical shape with a longitudinal sleeve thereon, the sleeve fitting over a central stud which is integral with the cap. The stud may be so dimensioned and shaped in cross-section, and the sleeve similarly shaped and dimensioned to prevent relative turning of the cap and gasket with respect to one another during opening and closing of a container with the closure.