Breathers are used for oil reservoirs that need to be ventilated.
When oil is moved for example by a gearing that runs in a oil bath, there may be the risk of leaking oil. With a filter (filled with acid-resistant stainless steel balls) the emission of oil-haze is avoided at these breathers, without affecting the ventilation (pressure compensation).
You can do the filters when their function is not needed or more air flow capacity is desired. With this novel ball-fill we achieve maximum protection against choking and easy cleaning while the air flow capacity is very high. Other screw threads on request.