PYREX 25mL Screw Cap Culture Tubes with PTFE Lined Phenolic Caps, 20x125mm. These 25mL PYREX culture tubes are supplied with deep-form 18-415 GPI threaded phenolic caps to facilitate handling and sealing after autoclaving. Caps are fabricated from a special formula resistant to the effects of temperature and steam in autoclaving and are provided with a Polytetrafluorethylene (PTFE) interface firmly bonded to the glued-in rubber liner, providing a sure and highly inert sealing face. The white enamel marking spot gives an excellent surface for pencil notations. Pencil marks are easily erased. For replacement phenolic caps, see No. 9998.