A fitting for the end of a fuel tank filler tube such as a plastic, blow molded filler tube in an automotive vehicle comprises:a flexible band adapted to be inserted into the end of the filler tube to form a locking ring lying against the inside surface of the filler tube, wherein a V-shaped gap between the ends of the locking ring taper to be more narrow in a direction inward the filler tube, the inner surface of the flexible band comprising first engagement means such as, for example, annular or spiral ridges or grooves;a wedge adapted to be inserted into the V-shaped gap between the ends of the locking ring to force the locking ring tightly against the inside surface of the filler tube; anda restrictor cup comprising a tubular side wall and a restrictor wall with an opening through it, adapted to be inserted into the filler tube, restrictor wall end first, to engage said locking ring, which restrictor cup comprises engagement means such as, for example, annular or sprial grooves or ridges adapted to engage the engagement means of the locking ring.The wedge is preferably integral with the restrictor cup such that as the restrictor cup is pressed into the end of the filler tube and is engaging the locking ring, the wedge is simultaneously acting upon the locking ring.