The invention relates to an arrangement (10) for assembling two parts (12, 14) by screw-fastening, characterized in that it comprises a horizontal flat first part (12) comprising a housing (44) which extends axially along a screw axis contained in the horizontal plane of the first part (12) and which houses the screw (18) and the nut (24), at least part (32) of which collaborates with a thrust surface (46) of the housing (44) so as to immobilize the nut (24) axially when a tightening force is applied, and a vertical second part (14) orthogonal to the first part (12) comprising a first bearing surface (50) and a second bearing surface (52) which bearing surfaces, in the assembled position, collaborate one of them with a reaction surface (54) of the first part (12) and the other with a clamping surface (56) of the screw (18), the threaded shank (22) of which passes through the second part (14) in such a way that part (28, 30, 130) of the screw (18) applies an axial clamping force to the said second bearing surface (54) in order to immobilize the first and second parts (12, 14).