material suitable for downhole use in a drilling environment the stator also comprises a liner 36 that may be formed from an elastomer a plastic or any other suitable synthetic or natural material known in the art in some embodiments the liner may also be formed from a fiber reinforced material such as the materials described in co pending u s patent application ser no 10 097 480 and assigned to the assignee of the present application the external tube 38 comprises a shaped inner surface 44 that comprises at least two lobes 46 formed thereon the lobes 46 are helically formed along a selected length of the external tube 38 so that the lobes 46 define a helical pattern along the selected length the helical form of the inner surface 44 generally corresponds to a desired shape for stator lobes the liner 36 typically comprises at least two lobes 40 and a thickness 42 of the liner 36 is non uniform throughout a cross section thereof the lobes 40 and the liner 36 are helically formed along a selected length of the external tube 38 such that the liner 36 conforms to the helically shaped inner surface 44 so that the at least two lobes 46 formed on the shaped inner surface 44 correspond to the lobes 40 formed in the liner 36 the external tube 38 including the inner surface 44 may be helically shaped by any means known in the art including machining extrusion and the like in some embodiments the shaped inner surface 44 of the external tube 38 is adapted to provide additional support for the liner material the shaped inner surface 44 u201c stiffens u201d the liner 36 by providing support for the liner 36 e g by forming.