Abstract: A chuck for polygonal shank ends of tools, has a bushing (5) which transmits the drive force and corresponds in its cavity (8) to the polygon cross section of the shank end (32). The bushing has a window-shaped opening in which a ball (22) is arranged as pressing member which acts on the shank. Behind the bushing there is arranged an actuating sleeve (11) which is displaceable against spring action and which lies in front of support shoulders in the region of the inner edge of the opening (23). In order to obtain an optimal form of use, the ball (22) is more than twice as great as the width of the corner recess (31) lying in the axial direction of the shank. The clamping surface (19) is inclined in wedge shape in the direction of action of the spring, and extends at an angle to the longitudinal axis of the chuck which lies within a self-locking region.