Ford called this part the fuel vapor separator. It mounts to the top of the fuel tank. This is part of the emissions control smog system, the fuel vapors that are collected in the charcoal canister are returned through a hose to this device into the fuel tank. Applications for this part include: 1971-73 Mercury Cougar and Ford Mustang, 1971-72 Pinto and Bobcat, 1971-72 Maverick and Comet, 1971 Thunderbird and Lincoln MKIII, and 1971-73 Ford / Mercury full sized cars. Starting about 1973, this part was made of plastic.
Ford part number D1AZ-9B328-A.
O-ring gasket or seal is available, as are new locking rings, and used locking rings.