The invention relates to a tool-holder mandrel for fitting to a rotating machine, comprising: a body comprising a rear portion designed to be attached to a drive shaft of the rotating machine and a front portion in which housing are arranged converging toward the front; jaws mounted so as to slide each in a housing of the body and having an inner thread; a ring for moving the jaws, mounted so as to pivot relative to the body, having a peripheral thread interacting with the inner thread of the jaws so that the rotation of the ring closes or opens the jaws.