apparatus for making profiled plastic tube and comprising two circulating endless chains , each making a plurality of mold halves move along with a tube coming from an extruder , these mold halves pairwise constituting a mold cavity in which the tube is being given its profile . according to the invention the molds are movable relative to the chain links in a direction perpendicular to the direction of movement of the links . the machine frame is provided with guides for the mold halves , some located interiorly , others exteriorly , with respect to the chain loop , such that once closed , the cavity formed by the pairs of mold halves will remain closed and undisturbed up to the end . preferably the transitions between curved portions and the operative portion of the path of the mold halves at the entrance and the exit ends are bending points of mathematically calculated paths and the operative straight path tangentially joins said transitional portions . in order to further eliminate vibrations and other disturbances in the regular course of the mold halves , it is preferable that the chains are each provided with driving means which are operative near the entrance end of the operative straight portion of the path , and with braking means which are operative near the exit end thereof .