FILL-RITE, 4 Diameter, Vented Fuel Tank Cap, FRTC Series, Silver/White The FILL-RITE FRTC is a vented fuel tank cap designed for use with above-ground fuel transfer and storage tanks. This cap is engineered to relieve dangerous vapor buildup and prevent over-expansion or contraction of the tank due to temperature changes. Constructed from high-quality materials, the FRTC offers durability and reliable performance in demanding environments. It also includes a hole and tab for padlock security, providing an added layer of protection against fuel theft or tampering.