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Abstract

A chuck comprises a body centered on an axis and adapted to be mounted on a drill spindle for rotation about the axis and a tightening sleeve carried on the body and rotatable thereon about the axis. The sleeve or body is formed centered on the axis with an array of angularly equispaced guides inclined to the axis and the other element is formed centered on the axis with a screwthread formation. Respective jaws are displaceable axially and radially of the axis in the guides relative to the axis and are formed with teeth meshing with the screwthread so that rotation of the sleeve relative to the body in one rotational sense moves the jaws axially forward and radially together and opposite rotation moves them axially backward and radially apart. A braking sleeve rotatable on the tightening sleeve has an inner surface engageable with the tightening sleeve and this inner surface can be pressed radially into engagement with the tightening sleeve.