Abstract: Thermoplastic polymer locking elements are formed on threaded fasteners to provide a range of self-locking torque characteristics. The thermoplastic resins are of the type that crystallize during cooling from the molten state.The crystallizable polymers are preferably applied in film form to preheated threaded fasteners. By correlation of the preheat temperature, the length of time during which the molten polymer is allowed to melt and flow onto the thread surfaces, and the rate of cooling of the assembly, the geometry of the locking element and the degree of crystallinity of the polymer are controlled.

Abstract: An externally screw threaded fastener body is bored longitudinally to form a bore having a reduced inner axial portion and an outer axial portion of enlarged diameter and a noncircular mandrel is forced into the bore to expand the reduced inner portion thereof and thereby form at least one radially outwardly protruding lobe for local increase in the pitch diameter of the external screw thread. The fastener body may then again be drilled longitudinally, the final result being a fastener, at least a portion of which is tubular with a relatively thin resilient circumferential wall having at least one radially outward lobe.