These are 20 ml clear borosilicate glass EPA vials that are 24mm 24-414. They are designed to be paired with screw on caps. Commonly used in the environmental industry, the borosilicate glass allows it to withstand a wide variety of different contents such as acids, pharmaceuticals, and alkalis. These vials are type 1 borosilicate, 33 expansion and are sold in packs of 144.