Abstract: A screw or tap for forming or cutting threads in a workpiece. The screw includes a cylindrical shank directed along a longitudinal axis. The shank includes a work holding portion having a plurality of helical threads of a constant crest diameter, a constant root diameter, a constant pitch diameter, and circular cross-section. The shank also has a lead portion having at least a portion of a helical thread. Intermediate the work holding portion and the lead portion is a forming portion. The forming portion has at least one full thread located thereon having a crest diameter which is greater than the crest diameter of the plurality of helical threads on the holding portion, a root diameter which is larger than the root diameter of the plurality of helical threads on the holding portion, and a pitch diameter which is proportionally greater than the pitch diameter of the holding portion.

Abstract: A radial extrusion thread-forming screw (20) comprises a lead thread (36), load-bearing threads (34), and a forming thread (38). The forming thread (38) has a plurality of forming elements (50) that extend outwardly from the forming thread and which are spaced substantially circumferentially equidistant from each other. The forming thread (38) is tapered about its circumference such that the first forming element (50) moves the greatest amount of material and subsequent forming elements (50) move successively less such that each of the forming elements require substantially the same deformation force to move through the workpiece. The forming elements (50) are of a geometry which promotes deformation along slip planes in the material of the workpiece. The lead thread (36) and the load-bearing threads (34) do not have any forming elements (50) located thereon.