Abstract: A boregrinding chuck assembly includes a plurality of arrow-shaped jaws that each includes a head that is in the shape of an isosceles triangle with the apex angle thereof just slightly less than 360.degree. divided by the total number of jaws in the assembly so that there is a small gap defined between adjacent jaws when such jaws are holding a workpiece in position for a boregrinding operation. Each jaw includes a set of marking lines that are located to define a workpiece-engaging circle that has a diameter just slightly smaller than the outer diameter of the workpiece to securely hold such workpiece when all of the jaws are engaged against the workpiece. The jaws are customized by cutting the heads along the marking lines that are appropriate to the particular workpiece.