The TN LAB 50 ml Volumetric Flask is made from Borosilicate 3.3 Glass. It has 50ml Class A Accuracy, +/- 0.05ml @20C, per ISO 1042-1998. The flask has a NS 12/21 ground joint PTFE plastic stopper to minimize sticking and seizing. Our glass volumetric flask has superior strength, durability, and chemical resistance. And most importantly is has an easy-to-read precise 50ml marking. 5-Pack of 50ml Borosilicate Glass Volumetric Flasks. Volumetric flasks measure one exact liquid volume. This 10ml volumetric flask will measure 10ml with Class A accuracy, precision to 0.05ml. In the neck of all volumetric flasks is a very thin line, the graduation line, indicating the fill point. A volumetric flask will only measure its designed volume. No other graduations or volume markings appear on volumetric flasks other than the graduation line, and they can't be used to measure any other volume.