one end of a collapsible cylinder having an impermeable side wall is shaped to form an impermeable shoulder and neck liner on which a polyethylene head can be molded . the end of the collapsible cylinder is crimped by a plurality of arms which are swung down simultaneously to form the end of the cylinder into a plurality of pleats , each pleat having a shoulder portion and a neck portion . each arm carries a prism like member which creases and partially folds over the pleats . this crimped cylinder is then removed to another location where a shoulder forming block descends axially on it to form the shoulder including a re - entrant edge at the outer periphery of the shoulder . a series of truncated , pie - shaped blocks are brought in radially to contact the pleats and complete the folding over of the pleats . the intermediate product thus formed is ready to have the plastic head molded onto it .