In some embodiments, a tool includes, in an injection molding machine, a movable internal core configured to receive a molded plastic layer thereon, the molded plastic layer having a thickness. The tool also comprises an injection nozzle configured to inject plastic material over the movable internal core to form the molded plastic layer; an ejection plate connected to the movable internal core; and multiple, movable support plates each having a thickness. The multiple, movable support plates are located behind the ejection plate. A movable support plate of the multiple, movable support plates is configured to determine the thickness of the molded plastic layer.