SP Brand Accutube Flange Caps Natural Cardinal Health Description: Made of polyethylene These caps have two flexible flangers to ensure a leakproof seal. They will fit into test tubes and also in round cuvettes and centrifuge tubes. AccuTube flange caps are made from non-autoclavable, low-density polyethylene. The flange seal allows easy opening and closure and provides a universal fit on 12 and 13mm test and culture tubes. Natural color. They feature two flexible flanges that press firmly against the inside wall of the tubes, thereby providing better leak-resistance than standard plug caps.