The large number of machinability tests developed in the past are limited by their ability to compare materials of different classes, e.g., ferrous vs. non-ferrous metals, and by the extrapolation of test data to machine shop practice. Publication of ASTM E618, a machinability test that evaluates materials under production-scale conditions using a commercial automatic screw machine, does provide the basis for making such a comparison and can offer practical information to the machinist. However the ASTM test method has heretofore been applied almost exclusively to steels or to metals of similar classes. A technique was therefore devloped whereby ASTM E618 can be applied to a number of different materials, including brasses, carbon and leaded steels and aluminum alloys. A graphical method of data analysis has also been developed which enables (1) formulation of a universal machinability rating by direct comparison of different materials and (2) prediction of both theoretical and actual production rates for arbitrary screw-machine products based on workpiece dimensions, workpiece material and the type of cutting tool employed. The test method and data analysis are described. Predicted production rates are compared with those experienced by a commercial screw-machine operator.