Method of making screws and dies therefor

摘要

Method and dies for threading a screw comprises providing a screw blank with a portion of its length of lobular cross section and an adjacent portion of the blank of circular cross section. The blank is rolled between roll dies so as to roll the thread on the circular portion and simultaneously roll the thread at the lobes only on the lobular portion. Thereafter, the blank is rolled to additional regions of the dies wherein the thread is rolled to form on the lobular section, while the cylindrical section passes through regions of clearance or relief on the dies.