*** NO LONGER AVAILABLE *** Crankcase breathers are used to vent contaminated oil and water mixture from your engine block into the atmosphere. Without a crankcase breather, this mixture is returned back into the engine directly or through the airfilter and can affect the air/fuel ratio causing a loss of power. Pipercross use a chemical resistant crushed aluminium filtration medium in all to-atmosphere breathers. Pipercross sealed in-line breather filters use a reticulated foam which can be cleaned for long life and efficiency. All are suitable for use with 13mm, 16mm or 19mm sized breather piping.