This plastic breather cap seals the fuel system on the host tractor, allowing air to enter or exit the tank as fuel level changes while blocking dirt and moisture. It screws into the filler neck or vent port of the fuel tank, maintaining atmospheric pressure inside the system. A clogged or missing breather can cause a vacuum lock that starves the fuel pump or allow contamination into the tank. The cap is manufactured to the original sealing geometry so it seats correctly in the fuel-system housing.