Abstract: The machine-tool drill chuck is comprised of a main cylindrical hollow body (2) linked by its rear end (13) to the machine tool and provided at its front end (15) with a front conical socket (7), inside which is located another socket (9) carriying clamping jaws (8) for holding the drill and which are subject to the action of a pushing screw (6) which is coaxial with the main body. Windows (12) are arranged as through openings in the main body. In each of the windows there is arranged a satellite gear (4) whose axis is parallel to the axis of the main body (2) and whose diameter is substantially larger than the thickness of the main body wall. The satellite gears are in mesh with the external toothing of a central gear (3) and with the internal toothing of an external ring (5) which may be actuated manually or with a key. Said central gear is also internally in mesh with the pushing screw.