Method and arrangement for angularly positioning a container or a container preform on a mandrel inserted in the neck thereof

A method of positioning a container or a container preform of thermoplastic material and having a neck with a substantially circular cylindrical inside wall, in a predetermined angular position on a mandrel, comprising

• providing at least one approximately radial projection on either the inside wall of the neck or the outside wall of the mandrel so that the projection can bear against at least one thrust shoulder provided on whichever of the outside wall of the mandrel or the inside wall of the neck does not have the at least one projection, said shoulder facing respectively towards the free end of the mandrel or the free end of the neck and extending over said wall on which it is positioned while being inclined relative to the axis of the mandrel or the axis of of said neck, respectively, and
• inserting the mandrel into the neck, thereby causing the neck to rotate relative to the mandrel, rotation being generated by said at least one radial projection sliding against said at least one shoulder, until locking means prevent relative movement of the mandrel and of the container or preform once the neck is disposed in said predetermined angular orientation relative to the mandrel.