The tank filler neck has a ring-form sleeve (4) encompassing it and which comprises a ring (4') and a collar (8) at right angles to it. The sleeve at one point has a break and a radially opposite-lying hinge-type element so that the collar is located between the hinge-type element and the break. The break in the sleeve is closed off by a plug-in connection installed on both sides of the break on the collar and ring. The hinge-type element has a groove which interacts with a nose on the filler neck.
