Abstract: A divided nut comprising two divided nut parts made of plastics which provide engaging projection means and engaging step means so as to engage with each other in a state of fixed fittings. The divided nut parts are integrally connected to each other by means of belt-like connecting means where they are bent to fit each other.

Abstract: A plastic pipe having spiral ridges on an outer surface and a continuous, cylindrical inner surface formed by a spiral wound plastic ribbon having at least one ridge-shaped hollow deformation extending longitudinally of the ribbon and spirally of the pipe. The outer radial surface of the hollow deformations are slit and sealed with a ribbon. Side portions extend from the opposite sides of the hollow deformations and are fused to each other to form the cylindrical inner surface.

Abstract: An apparatus for manufacturing a resin tube comprising: (a) a support means; (b) a central support by the support means and extending therefrom; (c) a pair of operating means supported by the central shaft at two separate positions; (d) a plurality of rotatable forming rolls each supported by the operating means at both ends thereof in such a manner that the rotatable forming rolls are arranged circularly around the central shaft and that a cylindrical envelope formed by the rotatable forming rolls has a radius changeable by operation of the operating means; and (e) a plurality of flexible link means each connected between one end of each rotatable forming roll and a driving means for simultaneously rotating the rotatable forming rolls in the same direction at any radius of the envelope. Because of this structure, the apparatus can manufacture a resin tube of any size simply by operating the operating means.

Abstract: A method of manufacturing a plastic pipe having a spiral ridge on an outer surface and a flat inner surface, comprising the steps of: (a) supplying a plastic ribbon in a softened state onto a plurality of rotating forming rolls arranged circularly, so that the plastic ribbon is spirally wound around the forming rolls while partially overlapping to be fused with each other; (b) spirally winding an endless forming core belt around the forming rolls in such a manner that the endless forming core belt is sandwiched between the plastic ribbon already wound around the forming rolls and the plastic ribbon newly supplied, thereby providing the resulting plastic pipe with a spiral ridge; (c) cutting the spiral ridge after the plastic ribbon is fused with each other and sufficiently cooled, thereby providing the spiral ridge with a slit extending along it to remove the endless forming core belt from it; and (d) winding a second plastic ribbon in a softened state around the spiral ridge to fuse the second plastic ribbon