These high performance Rotaflo® 90° angle stopcocks can be adjusted. They are designed so that only chemically resistant Polytetrafluoroethylene (PTFE) and PYREX® borosilicate glass are in contact with liquids and gases. The Rotaflo® stopcock design permits fine flow adjustment. Lubrication is not required and assembly is fast because there are no O-Rings, washers or nuts. The seal is visible when open or closed.