Polypropylene 1.1 ml V-bottom tubes have internal threads that accept screw caps for secure closure in ultra low temperatures. The polypropylene screw caps (sold separately) have silicone O-rings that maintain their integrity in vapor phase liquid nitrogen. Certified RNase and DNase free and manufactured to Class 10,000 regulations. Working volume: 0.8 ml with cap when freezing. Non-coded tube. Replaces item 1765-2318.