Rubber Stoppers
Sargent-Welch black gum rubber stoppers are specially compounded to achieve the resiliency, softness, durability and gripping qualities most favorable to chemical laboratory requirements. These stoppers are recommended for all general applications because of their very low sulfur content. Sizes are standardized with size numbers molded into the top of each.

• XXXX Quality Corks have a fine grain and are ideal for use as tight-fitting stoppers. Sizes listed are normally used in school science laboratories. Regular length corks.
• XXX Quality Corks have slightly irregular cavities but are suitable for use as bottle stoppers and most school laboratory stopper requirements. Regular length corks.