Keep your air sanitary! This in-line sanitary filter can filter down to 0.023 microns, which will take care of most microbiological agents that could potentially contaminate beer. The filter has a 3/8" fitting on either side. It is most often used in-line for aeration systems, such as those utilizing aquarium pumps or in keg hand pumps. They can also be used in CO2 systems when CO2 is used to pressurize a fermenter or used to purge the headspace in fermenters or kegs in order to keep contaminants from the tank out of your beer. These sanitary filters should be kept dry.and should be always be used in the same direction, the "in" side always being in and the "out" side always being out.