rubber stopper

A rubber stopper is a small, tapered plug used to seal the openings of test tubes, flasks and other laboratory glassware. Stoppers made of cork are also available for this purpose. However, rubber stoppers are preferable for applications that require a tighter seal or a greater degree of chemical resistance.
Rubber stoppers act as corks for bottles of wine and champagne. They also work as plugs in a variety of applications such as trapping and containing solvents. Manufacturers make certain types of stoppers with silicone for temperature-sensitive work. Other uses for rubber stoppers include using stoppers as clamps, door stoppers, grippers and bumpers.
Chemists use rubber stoppers to prevent not only liquids but also gases from escaping from vials and test tubes during reactionary work. Rubber stoppers work quickly to hold liquids and gases in places without any time loss involved in screwing on a cap or lid.
Another use for rubber stoppers is for the manufacture and transportation of prescription drugs. Specially designed rubber stoppers reduce interaction between the stopper's materials and the ingredients used in the drug's manufacture. Stoppers keep the prescription drugs in glass vials during the drug manufacturing process so as to prevent leaks, hazards and contamination.
Depending on the type of project, a chemist needs a rubber stopper with or without holes. For certain types of chemical reactions, gas in the test tube creates pressure that breaks the test tube's glass, if the reaction does not have proper ventilation. A rubber stopper with ventilation holes prevents this type of problem during chemistry work.