A carriage unit for sliding doors or windows of the lift and slide type, the door or window comprising at least one fixed frame and a sash horizontally slidable relative to the frame, between an open position and a closed position; said carriage unit comprising at least one main carriage (4, 5), associated, in use, with the bottom crosspiece of the sash and resting on a horizontal base track to allow the sliding of the sash in both the opening and closing directions; the main carriage comprising a first box-type frame having an upper portion designed to be slidably coupled, in use, to the lower crosspiece of the sash and a second frame supporting a pair of wheels (10, 11) positioned, in use, resting on the track; the main carriage (4, 5) having a drive linkage of the movement comprising at least one operating arm interposed and connected, in use, between and to a rod of the carriage unit slidable in the sash and means for lifting and lowering the sash positioned and acting on the main carriage (4, 5); on the rod is coupled an end defining a fixed end point of secure connection with a connecting means between the rod and the operating arm; the end being slidably insertable, in use, in the sash; the sash being connected, in turn, to a handle; the handle being connectable, in turn, to the rod and positioned on the sash for controlling the open position, with a lifting of the sash relative to the track, and the closed position, with a lowering of the sash relative to the track by rotating the handle from a first configuration to a second configuration, and vice versa, in such a way as to also activate the means for the lifting and lowering; the means for lifting and lowering the sash being in form of a link mechanism positioned and acting between the first frame and, in use, the operating arm controlled by the handle positioned on the sash; characterised in that the operating arm of the drive linkage has adjustable connecting means for its secure connection with the rod; the adjustable connecting means being designed for adapting the position of the arm relative to the rod keeping unchanged the position of the rod and the relative configuration adopted by the handle and by the lifting and lowering means of the main carriage (4, 5); the adjustable connecting means comprising a slide articulated with the operating arm and designed for the contact and the front joining with the end connected to the rod and means for adjusting the relative position between the end and the slide positioned between the two contact surfaces (26a, 27a) of the end and of the slide, so as to allow a modification of the position of the slide relative to the end varying the angle of inclination of the operating arm relative to the rod and the lifting and lowering means; wherein the adjustable connecting means also comprise means for clamping the slide to the end and designed for locking the slide to the end in the defined position and wherein the adjusting means comprise a toothed surface and a counter-toothed surface made on the corresponding front contact surfaces of the slide and of the end which can be coupled to or co-penetrated in each other to allow a plurality of relative separate positions between the slide and the end.