Method of injection molding closure with continuous internal rigid rib, closure made thereby having a lead-in structure and mold for forming same

An injection molded container closure with a continuous internal projection, in particular a rib having a length-to-width ratio of at least one and one-half, is formed with a mold cavity between a pair of mold halves. One mold half includes a core forming the interior of the closed annular structure of the container closure, wherein the core is separated into a movable core portion and a remaining core portion at a separating line defined at the internal rib for forming the same.