These high performance Rotaflo® in-line stopcocks 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.