Abstract: Rib-fitting as a component (9) of a torsion box (1, 3) of an aircraft lift surface made of composite material as a single piece, comprising: a substantially planar web (31) with a first part in the form of a lug (33) and a second part in the form of a rib web (35); two flanges (39) to attach the web (31) with the webs of each of the ends of the front or back spar (11, 13) to which it is joined; flanges (43) for being attached to the upper and lower skins (19, 21) of the torsion box; gaps (45) in the areas of intersection with the front or back spar caps (11, 13) to which the component (9) is connected and with the reinforcement stringers (25) of the skins (19, 21). The invention also comprises and assembly process for the rib-fitting in multispar torsion boxes.