This is a the hard metal pipe with the nut and nipple (that is soldered to pipe) which connects the outlet of the Fuel Pump forward. On the MGB 1963 to 1969 the line goes up to the carburetor hose connector. On the MGB 1970 to 1974 it connects to a shorter hardline at the front of the car. With years of use this pipe gets damaged and kinked, which equals low fuel flow. Low fuel flow is low horsepower, which is not good. Replace your line when you change your fuel tank. Since the pipe comes in a roll, some find it easier to use a tub bender to clean bends, other are fine with homemade options like bending around large sockets work well too.