Abstract: To provide for an axially short self-tightening chuck, a spiral spring (22) is located inside the chuck to couple together a cylindrical surface (24) formed on the chuck spindle, for example on an extending flange (17) thereof and a cylindrical surface (25) on an axial extension (16) of a holding sleeve which retains the chucking mechanism, including clamping jaws (9) and the like. An operating ring (23) is engageable with an end portion of the spring. The spring has a direction of winding which, with a given direction of rotation of the tool, tightens the spring about the axially adjacent surfaces (24, 25) on the chuck body and the holding sleeve, so that they will rotate together, and, even under conditions of vibrations or sudden stopping, not loosen, since relative reverse rotation is inhibited by frictional engagement of the spiral spring between the parts.