Sheet metal fasteners

Claim 1

A METALLIC FASTENER FOR ATTACHMENT TO A WORKPIECE HAVING AN APERTURE THEREIN, SAID FASTENER INCLUDING, A BODY OF MATERIAL WHICH IS HARDER THAN THE MATERIAL OF THE WORKPIECE AND HAVING A PILOT FLANGE OF APPROXIMATELY THE SAME DIAMETER AS THE DIAMETER OF THE APERTURE IN THE WORKPIECE IN WHICH IT IS TO BE MOUNTED, SAID BODY HAVING AN ABUTMENT FLANGE, SAID FLANGES BEING SPACED APART BY AN AXIAL WALL ON SAID BODY TO DEFINE AN ANNULAR RECESS HAVING UPPER AND LOWER WALL PORTIONS CONSTITUTED, RESPECTIVELY, BY A PORTION OF THE UNDERSIDE OF SAID ABUTMENT FLANGE AND THE UPPER SIDE OF SAID PILOT FLANGE AND EXTENDING GENERALLY NORMAL TO THE AXIS OF SAID BODY, SAID ABUTMENT FLANGE BEING PROVIDED WITH TEETH EXTENDING AROUND THE OUTER PERIPHERY THEREOF ADAPTED TO BE EMBEDDED IN THE METAL OF SAID WORKPIECE TO POSITIVELY LOCK SAID ABUTMENT FLANGE AND SAID BODY AGAINST ROTATION RELATIVE TO SAID WORKPIECE, SAID TEETH BEING DEFINED BY SURFACES WHICH MERGE TO FORM GENERALLY AXIALLY EXTENDING EDGES, SAID ABUTMENT FLANGE HAVING A DIAMETER, EXCLUSIVE OF SAID TEETH, THAT IS SUBSTANTIALLY GREATER THAN THE DIAMETER OF SAID PILOT FLANGE TO CAUSE SAID ABUTMENT FLANGE TO OVERLIE A SUBSTANTIAL PORTION OF THE SURFACE OF SAID WORKPIECE SURROUNDING SAID APERTURE, THE ENDS OF SAID TEETH INCLUDING AXIAL PORTIONS THAT EXTEND THEREFROM SLIGHTLY BEYOND THE