Abstract: Conduit means characterized by having a plurality of parallel adjacent, longitudinally extending passageways within an exterior wall and having longitudinally extending ribs extending longitudinally of and exterior to the exterior wall for high flexural strength and high strength enabling bearing high external loads. The passageways have at least a portion of their interior walls in common with adjacent passageways. Preferably, the conduit, including the ribs, are formed of a lightweight, extrudable plastic. Also disclosed are structural details, apparatus, and methods, including one for making any number of passageways in the conduit.