Cork Stopper

Each cork stopper is tapered, with a larger diameter at the top and a smaller diameter at the base. They are sold in three sizes:

• No. 6: 13mm x 19mm x 24mm (H)
• No. 11: 21mm x 27mm x 31mm (H)
• No. 12: 22mm x 29mm x 31mm (H)

Choosing a cork for a test tube

The cork to use depends on the tube's opening diameter. Common test tube sizes are around 20-25 mm in diameter and 100-150mm in length. Corks are typically chosen for a snug fit, where the bottom diameter of the cork is the largest size smaller than the test tube opening. 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 a natural, compressible material that creates a tight seal to prevent contamination and evaporation. It is also a good insulator and relatively non-reactive. It contains samples and maintains pressure, and is a compromise between a completely sealed system and one that allows for gas exchange.