Abstract: Standard chemical laboratory glassware taper joints are retained by a threaded cap which, when screwed onto a male threaded part surrounding the female standard taper element with an O-ring surrounding the glassware part at the shoulder of the standard male taper holds the tapered surfaces together under resilient pressure to maintain tight closure at the taper interface. The O-ring, being compressed between the threaded retainer cap as the applied force, and the shoulder of the male taper element and the top of the male threaded part, as force receiving surfaces, provides a backup seal for the joint.