0 mm wide with a channel mouth at the surface 50 being approximately 4 0 mm wide whereas the aforementioned recesses or flats of the zweifel publication extend slightly onto the unthreaded portion of the neck they do not extend far enough to reach any restriction in the filler e g at a location of the hinge of the flapper in the single flapper embodiment illustrated and the outer of two flappers in the two flapper embodiment with the channels 52 long enough to pass adjacent any chokepoint in the filler the channels may serve as vents to vent vapor from the tank and thereby speed the emptying of the bottle even if there is nominal clearance between the outer diameter surface of an ungrooved neck and the inner diameter surface of the filler misalignment deformation of the neck i e the bottle axis 500 is rotated off parallel to the filler axis may contribute to airflow blockage and thus hinder bottle emptying by providing the channels 52 emptying is facilitated despite misalignments in the exemplary embodiment the channels 52 extend along a straight essentially untapering upper portion 70 fig1 of the unthreaded portion 50 and a downwardly divergent portion 72 therebelow this divergent portion 72 has a small half angle u03b8 e g about 2 u00b0 in the context of a standard size capless filler the exemplary diameter at the unthreaded portion upper portion 70 is 21 69 mm transitioning to 22 69 mm at the base of the divergent portion at the groove lower ends 56 a more broad example of diameter is 20 0 mm to 25 0 mm.