Apparatus and a method for permanently joining integrally formed plastic screw conveyor modules is disclosed. A support means supported by a base supports a multiplicity of previously joined modules. A holding means also mounted to the base supports a single module to be joined to the already joined modules. The holding means supports the single module such that the axial member of the single module is aligned with the axial member of the multiplicity of modules. A melting means such as a heating plate is placed in firm contact between the ends of the modules to be joined until the plastic begins to melt. The heating plate is then removed and the modules while being supported firmly along their axis are pressed together and maintained in such a position until the melted plastic begins to solidify and thereby joining or bonding the single module to the already joined modules.