Abstract: A method and apparatus therefor using the stress wave phenomenon for sizing and working a hole in a workpiece. A mandrel of the desired size, shape, and finish is "driven" into the hole by a stress wave to work the hole and impart thereto a desired shape, size, and finish. Electromagnetic means are used to generate the stress wave whose characteristics are such that it can be propagated through the mandrel and into the workpiece with a pulse energy level, rise rate, and duration sufficient to put the material in the walls of the hole into a condition of plastic flow so that a permanent deformation thereof conforming to the working area of the mandrel is achieved. A straight or a tapered hole can be worked or a straight hole can be converted into a tapered hole having the desired final shape, size, and finish. In a further embodiment, the mandrel used in the method can be the fastener for which the hole has been drilled.