Abstract: A method of manufacturing a hollow body such as a golf club head, having an external hollow body of molded thermal plastic material and an insert in the hollow by which it is possible to adjust the position of the center of gravity and the weight of the hollow body. An insert which is to remain within the hollow body is overmolded with a soft fusible metal to define with the insert a shape for the interior hollow of the hollow body. The hollow body of plastic material is overmolded over the combination of the insert and the overmolded core. The insert is then melted without melting the hollow body around it, and the melted insert material is removed from within the hollow body. For holding the insert and/or the fusible material core in place during the overmolding, either the insert is so shaped or a pin passes through the overmolded region defining an opening in the molded body through which the fusible material may be removed later, and that opening may be plugged.

Abstract: A pump rotor for displacing fluids includes a cover and a bottom part having blades. Both the bottom part and the cover are formed by injection molding of thermoplastic materials, preferably reinforced by fillers. The bottom part and the cover are joined together by welding. The walls of the bottom part and cover are sufficiently thin to replace similar metal parts and to provide maximum benefit of the skin effect resulting from the specific surface qualities of the molded material forming the bottom part and the cover. A mold for molding the bottom part and the cover is equipped with a cap which is angularly and vertically adjustable making it possible for a balancing weight to be fitted on the molded parts. The balancing weight is also angularly adjustable and has an adjustable mass.