Self-drilling sheet metal screw

Claim 1

A RESILIENT ONE-PIECE SCREW FASTENER OF METAL IN SHEET FORM HAVING A TRANSVERSE CROSS-SECTION IN SUBSTANTIALLY THE FORM OF A Z SHAPE WITH A CENTRAL MEMBER BEING RELATIVELY STIFF AND HAVING A TAPERED POINT AT ONE END THEREOF AND THE OTHER TWO LEGS OF THE Z BEING ARCUATELY CURVED TO FORM A PAIR OF OPPOSED INTERRUPTED SURFACES SPACED FROM THE CENTER MEMBER BY LONGITUDINALLY EXTENDING GROOVES AND DEFINING THE CIRCUMFERENTIAL EXTENT OF THE FINAL SCREW, THE CURVED SURFACES BEING PROVIDED WITH EXTERNAL PARTIAL THREADS EXTENDING COMPLETELY ACROSS EACH OF SAID SURFACES THROUGHOUT A MAJOR PORTION OF THEIR AXIAL EXTENT, AND THE ENDS OF THE CURVED SURFACES BEING PROGRESSIVELY TAPERED IN A MANNER CORRESPONDING TO THE TAPER OF THE CENTER MEMBER TO FORM A SUBSTANTIALLY CONICAL PENETRATING TIP BEING INTERRUPTED BY SAID LONGITUDINAL GROOVES, AT LEAST ONE THREAD ON EACH OF SAID CURVED SURFACES ADJACENT THE CONICAL TIP BEING SLIGHTLY TAPERED, THE EDGES OF THE CENTER MEMBER BETWEEN THREADS BEING DEVELOPED AS CUTTING EDGES WHEREBY WHEN DRIVEN THE SCREW CUTS ITS OWN HOLE AND PRESSES FIRMLY TO MAINTAIN CONSTANT TIGHTNESS WITH THE MATERIAL INTO WHICH IT IS SCREWED AND EJECTS CUTTINGS FORMED BETWEEN THE CENTER MEMBER AND THE TWO CURVED MEMBERS, EACH OF SAID OTHER TWO LEGS HAVING RADIALLY OUTWARDLY EXTENDING FLANGE PORTIONS AT THE OPPOSITE END THEREOF DEFINING A DRIVING MEANS THEREBETWEEN.