Abstract: A headed multi-lobed blank, method of manufacturing a self-tapping screw from the blank, and resulting multi-lobed self-tapping screw for joining thin workpieces provides desirable thread-forming characteristics at the conical tip and body portions, and improved resistance to vibrational loosening near the head. The resulting screw, obtained from the blank and method, incorporates a threaded tapered root portion between the screw head and body portion having a cross section that varies from nearly circular in the area adjacent to the underside of the head to a maximum out-of-round (or lobular) cross section at the intersection of the tapered root portion and the screw body.

Abstract: The device uses a diaphragm cover between the adapter and the die to lock the die into the adapter. The cover is rotatably mounted onto the adapter and has a polygonal bore that matches the polygonal bore of the adapter. The mandrel of the die has a throat in which the cover sits when the cover is in the locked position. The cover is biased with a spring into the locked position. Stops are provided to limit the movement of the cover between the open and closed positions.