Sample Tube Caps With External Threads are made of polypropylene. A long skirt and fast thread design allow the user to remove a cap with a single twist.
Closures on the matching tubes are also made of polypropylene, creating an identical coefficient of expansion. The matching coefficients maximize the leak proof seal at changing temperatures. Caps can be ordered with or without a silicon washer between the cap and the tube. Caps with a washer should be chosen when a positive seal is essential at a variety of temperatures.
The caps come in nine distinct colors for easy visual classification. They are designed for use in the storage and transport of biological materials. Caps can be ordered in lots of 1000.