Filler caps seal filling ports in tanks and reservoirs holding liquids or granular media. They prevent the ingress of foreign materials into and the leakage of fuel or media from the reservoir. Filler caps and fuel caps are an essential device on many vehicle reservoirs and storage containers, especially those holding combustible material. Many designs ventilate the reservoir to relieve pressure or vapor, while others provide an airtight seal. Closing methods include fine and coarse threads, quarter-turn connections, and a hinged radial or face seal.
