Abstract: The chuck assembly comprises: a chuck body having an outer end portion, an outer periphery and a central axial bore extending at least part way therethrough; a nose collar mounted on the outer end portion of the chuck body; structure for mounting the chuck body onto the outer end of a shaft of a powered drive mechanism; the outer end portion of the chuck body having at least one radially extending bore therein which extends from the outer periphery of the chuck body inwardly to an opening which opens to the central bore and which has a diameter less than the diameter of the radial bore; at least one ball or detent in the at least one radial bore; urging mechanism for urging the ball or detent into the radial bore and part way through the opening; releasing mechanism for allowing the ball or detent to move radially outwardly in the radial bore and away from the opening; and structure in the central bore for engaging a tool shank and preventing rotation of the tool shank relative to the chuck body.