PFA. Cap with S 40 buttress thread and screwable frit made of PTFE. A pore size of approx. 3 µm for optimal pearling of the gas into the liquid. A wide field of application is possible due to the use of high-quality fluoroplastic. Suitable only for non-pressurised operation. PFA. Cap with S 40 buttress thread and screwable frit made of PTFE. A pore size of approx. 3 µm for optimal pearling of the gas into the liquid. A wide field of application is possible due to the use of high-quality fluoroplastic. Suitable only for non-pressurised operation.