Abstract: The device is a clamp (1), designed to hold a construction piece, including a clamping lever (2), which climbs by pivoting around a transverse axis (3), in a case (4) formed by two half-shells (4a, 4b) with mirror symmetry along their joining plane and containing the clamping mechanism of the device (1), which is operated, by an intermediary shaft of a fluid cylinder (6) and (7) and of a system of a connecting rod (8) and a crank (9), or directly, between two positions, the first activates the release of the piece and the second activates the clamping of the piece, characterized in that each of the two half-shells (4a, 4b) forming the case (4) are made of a material that includes at least one reinforcement insert (10) made of a distinctively more rigid material and inserted into each half-shell (4a, 4b) in a zone subjected to high stress during clamping, so as to confer a resistance to stress in that zone, augmented in torsion, traction, or compression.