These PE flange plug caps are available in six colors for easy identification and color coding of samples, and have two flexible flanges to ensure a leakproof seal. These stoppers are made for our Disposable Polystyrene Culture Tubes and Disposable Polypropylene Culture Tubes, but will also fit into other test tubes and round cuvettes or centrifuge tubes. Match the cap size with the neck finish or top I.D. of your test tubes for proper compatibility.