Expansible hollow rivet having a polygonal shank

Claim 1

AN EXPANSIBLE HOLLOW RIVET COMPRISING (1) A HEAD AND (2) AN INTEGRAL AXIALLY-EXTENDING PERIPHERALLY CONTINUOUS SHANK HAVING A POLYGONAL EXTERNAL CONFIGURATION WITH APLURALITY OF PLANAR PARALLELOGRAM FACES EXTENDING CONTINUOUSLY FROM THE HEAD ALONG THE SHANK IN PARALLEL RELATION TO THE LONGITUDINAL AXIS OF THE RIVET WITH ADJACENT FACES MEETING IN CORNERS AT THE INTERSECTION OF THEIR PLANES, (3) SAID SHANK INCLUDING AN OUTWARDLY EXPANSIBLE PORTION ADJACENT AND EXTENDING AXIALLY IN THE DIRECTION AWAY FROM SAID HEAD TO A HOLLOW NON-EXPANSIBLE PORTION OF THE SHANK SPACED FROM SAID HEAD, (4) THE OUTWARDLY EXPANSIBLE PORTION HAVING A CENTRAL BORE OF CIRCULAR CROSS-SECTION EXTENDING AXIALLY THERETHROUGH TO A CONCENTRIC BORE OF LESSER DIAMETER IN SAID NON-EXPANSIBLE PORTION OF THE SHANK PROVIDING (5) A NON-UNIFORM WALL THICKNESS IN SAID EXPANSIBLE PORTION AND IN SAID NON-EXPANSIBLE PORTION WHICH CONTINUOUSLY INCREASES PERIPHERALLY FROM A MINIMUM AT THE ZONES MIDWAY THE CORNERS THEREOF TO A MAXIMUM AT SAID CORNERS, (6) THE NUMBER OF SAID PLANAR PARALLELOGRAM FACES BEING SUCH THAT, WHEN THE PERIPHERALLY CONTINUOUS WALL OF SAID EXPANSIBLE PORTION IS RADIALLY OUTWARDLY BULGED TO CONTACT A SIDE OF THE WORK, THE BULGED PORTION HAS A POLYGONAL EXTERNAL PERIPHERY AND MAXIMUM CLAMPING FORCE IS EXERTED LOCALLY ON THE WORK AT THE SAID CORNERS OF THE BULGED WALL, WHILE THE EXTERNAL SURFACE OF THE BULGED WALL BETWEEN EACH PAIR OF CORNERS AND FACING THE WORK HAS A SLIGHTLY CURVED CONTOUR IN THE AXIAL DIRECTION AWAY FROM THE WORK BUT THE OPPOSITE EXTERNAL SURFACE BETWEEN SAID EACH PAIR OF CORNERS HAS A CURVED CONTOUR IN THE OPPOSITE AXIAL DIRECTION.