Cork Stopper

Cork specifications for test tubes depend on the tube's opening diameter, with common test tube sizes being around 20-25 mm in diameter and 100-150mm in length. Corks are tapered with a wider top and a narrower bottom and are typically chosen based on a snug fit where the bottom diameter of the cork is the largest size smaller than the test tube opening.

Key specifications for corks

Tapered shape: Corks are tapered, meaning they have a larger diameter at the top and a smaller diameter at the base. 

Tapered dimensions: A typical example is a cork with a bottom diameter of 20 mm and a top diameter of 25 mm, suitable for a test tube with an opening of approximately 21-24 mm. 

Why is cork used to plug test tubes

Cork is used to plug test tubes because it is a natural, compressible material that creates a tight seal to prevent contamination and evaporation, while also being a good insulator and relatively non-reactive. Its properties make it ideal for containing samples, maintaining pressure, and allowing for a compromise between a completely sealed system and one that allows for gas exchange.