Plastic drive fastener having a radially collapsible shoulder

Claim 1

A ONE-PIECE PLASTIC DRIVE FASTENER COMPRISING AN AXIALLY ELONGATED SHANK INSERTABLE INTO A COMPLEMENTARY WORKPIECE APERTURE HAVING A PREDETERMINED CIRCUMFERENCE, AND A RADIALLY ENLARGED PORTION AT ONE END OF THE SHANK PROVIDING A FIRST SURFACE TRANSVERSE TO THE AXIS OF SAID SHANK FOR ENGAGING ONE SIDE OF THE MARGINS OF SAID WORKPIECE SURROUNDING SAID APERTURE, SAID SHANK INCLUDING A PORTION OF INCREASED DIAMETER RELATIVE TO THE DIAMETER OF THE SHANK PORTION ADJACENT SAID FIRST SURFACE TO PROVIDE SHOULDER MEANS SPACED FROM SAID FIRST SURFACE FOR ENGAGING SAID WORKPIECE AND RESISTING WITHDRAWAL OF THE FASTENER FROM THE WORKPIECE WHEN THE SHANK HAS BEEN INSERTED INTO THE WORKPIECE APERTURE, SAID SHANK INCLUDING A TAPERING ENTERING END PORTION EXTENDING FROM SAID SHOULDER MEANS AND TERMINATING IN A CIRCUMFERENTIALLY CONTINUOUS SOLID TIP FOR FACILITATING APPLICATION OF THE SHANK TO THE WORKPIECE, SAID SHANK HAVING LATERALLY OPENING SLOT MEANS THEREIN EXTENDING FROM ADJACENT SAID SOLID TIP TOWARD SAID FIRST SURFACE TO EXPOSE A CIRCUMFERENTIALLY CONTINUOUS UNINTERRUPTED SHANK PORTION FROM SAID SLOT MEANS TO SAID FIRST SURFACE, SAID SLOT MEANS BEING DEFINED BY GENERALLY AXIALLY EXTENDING SIDE SURFACES POSITIONED ON OPPOSITE SIDES OF THE SHANK AXIS AND A BOTTOM WALL CLOSING SAID SLOT, SAID SIDE SURFACES DIVERGING WITH RESPECT TO EACH OTHER SUBSTANTIALLY FROM SAID BOTTOM WALL TO INTERSECTIONS WITH A PERIPHERAL SURFACE OF THE SHANK, SAID SIDE SURFACES JOINING SAID BOTTOM WALL CLOSELY ADJACENT TO A PLANE CONTAINING THE AXIS OF SAID SHANK WHEREBY SAID SLOT BOTTOM PROVIDES AN AXIALLY EXTENDING RESILIENT HINGE RIB INTEGRALLY JOINING AXIALLY EXTENDING MARGINS OF ELEMENTS OF THE SHANK SEPARATED BY SAID SLOT MEANS AND WITH THE THICKNESS OF THE SHANK MATERIAL WHICH FORMS THE HINGE RIB BETWEEN THE BOTTOM OF THE SLOT MEANS AND THE OPPOSED OUTER SURFACE OF THE SHANK AT SAID SHOULDER MEANS AND AT LEAST ADJACENT THERETO IN A DIRECTION BOTH TOWARD SAID FIRST SURFACE AND SAID TIP BEING OF A MINIMUM THICKNESS RELATIVE TO THE CROSS-SECTION OF ADJACENT PORTIONS OF THE SHANK ELEMENTS ON OPPOSITE SIDES OF SAID RIB TO CONCENTRATE FLEXING OF THE SHOULDER MEANS ALONG THE RIB AS THE ADJACENT SHANK ELEMENTS ARE MOVED TOWARD AND AWAY FROM ONE ANOTHER, THE INTERSECTIONS OF SAID SIDE SURFACES WITH SAID PERIPHERAL SURFACE CONVERGING IN AN AXIAL DIRECTION FROM SAID SHOULDER MEANS BOTH TOWARD SAID FIRST SURFACE AND SAID TIP UNTIL THEY JOIN TO DEFINE AN OPENING WHICH HAS A MAXIMUM WIDTH IN THE VICINITY OF SAID SHOULDER MEANS, AND WHICH DIMINISHES IN WIDTH BOTH TOWARD SAID FIRST SURFACE AND SAID TIP, SAID SLOT HAVING A MAXIMUM DEPTH IN THE VICINITY OF SAID SHOULDER MEANS SUBSTANTIALLY GREATER THAN ONE-HALF OF THE MAXIMUM SHANK DIAMETER, SAID BOTTOM INCLINING FROM SAID POINT OF MAXIMUM DEPTH TOWARD SAID FIRST SURFACE AND SAID TIP AND THE OPPOSITE END SURFACES OF THE SLOT MEANS INTERSECTING SAID PERIPHERAL SURFACE, SUBSTANTIALLY ALL TRANSVERSE PERIPHERAL SURFACE PORTIONS OF SAID SHANK WHICH ARE INSERTABLE INTO SAID WORKPIECE APERTURE HAVING A CIRCUMFERENCE, EXCLUSIVE OF SAID SLOT SURFACES, NOT IN EXCESS OF THE CIRCUMFERENCE OF THE WORKPIECE APERTURE.