3/8" MNPTF x 3/8" FNPTF Aluminum Anti-Siphon Valve | EVM A/S 173 EVM A/S 173 Anti-Siphon Valve 3/8 in. Male NPTF x 3/8 in. Female NPTF Aluminum Anti-Siphon Valve 170 Series Designed to prevent the siphoning of marine fuel tanks should a fuel line leak or break occur