Screw fastener having preassembled clamping and sealing washers

Claim 1

A PREASSEMBLED FASTENER UNIT COMPRISING A METAL SCREW INCLUDING AN ELONGATED THREADED SHANK AND AN ENLARGED HEAD TERMINATING ONE END OF SAID SHANK, A SHOULDER HAVING A RADIALLY EXTENDING SURFACE CARRIED BY SAID ONE END OF SAID SHANK IMMEDIATELY ADJACENT TO AND FORWARDLY OF SAID HEAD, A CLAMPING WASHER FORMED OF YIELDABLE SHEET METAL AND CARRIED BY SAID ONE END OF SAID SHANK IMMEDIATELY ADJACENT TO SAID SHOULDER AND FORWARDLY OF SAID HEAD, SAID CLAMPING WASHER COMPRISING AN ANNULAR CONICAL BODY HAVING PARALLEL FRUSTO-CONICAL TOP AND BOTTOM SURFACES AND A CENTRALLY DISPOSED OPENING THERETHROUGH AND LOOSELY SURROUNDING SAID ONE END OF SAID SHANK, A SEALING WASHER FORMED OF RESILIENT SHEET MATERIAL AND CARRIED BY SAID ONE END OF SAID SHANK IMMEDIATELY ADJACENT TO AND FORWARDLY OF SAID CLAMPING WASHER, SAID SEALING WASHER COMPRISING AN ANNULAR FLAT BODY HAVING A CENTRALLY DISPOSED APERTURE THERETHROUGH AND TIGHTLY SURROUNDING SAID ONE END OF SAID SHANK, WHEREBY SAID SEALING WASHER IS FRICTIONALLY SECURED TO SAID ONE END OF SAID SHANK INDEPENDENTLY OF SAID CLAMPING WASHER AND SAID CLAMPING WASHER IS RETAINED IN ASSEMBLED RELATION UPON SAID SHANK JOINTLY BY SAID HEAD AND BY SAID SEALING WASHER, A FORWARDLY TAPERED EXTERNAL ANNULAR CENTERING SURFACE CARRIED BY SAID SHOULDER, A FORWARDLY TAPERED INTERNAL ANNULAR CENTERING SURFACE CARRIED BY SAID CLAMPING WASHER WITHIN SAID OPENING, SAID EXTERNAL CENTERING SURFACE COOPERATING WITH SAID INTERNAL CENTERING SURFACE AS SAID SCREW IS TIGHTENED TOWARD THE COOPERATING WORKPIECE SO AS POSITIVELY TO INSURE CENTERING OF SAID CLAMPING WASHER WITH RESPECT TO THE AXIS OF SAID THREADED SHANK, THE BODY OF SAID CLAMPING WASHER BEING FORWARDLY DISHED AND HAVING THE OUTER PERIPHERY THEREOF INITIALLY EXTENDING BEYOND THE OUTER PERIPHERY OF SAID SEALING WASHER AND INITIALLY CONTACTING SAID SEALING WASHER AT THE OUTER PERIPHERY THEREOF, THE BODY OF SAID CLAMPING WASHER BEING READILY YIELDABLE IN COMPRESSION BY THE ENGAGEMENT THEREOF ADJACENT TO SAID OPENING WITH SAID SHOULDER WHEN SAID SCREW IS TIGHTENED TOWARD A COOPERATING WORKPIECE, THEREBY TO CAUSE SAID CLAMPING WASHER PROGRESSIVELY TO COMPRESS AND TO DEFORM SAID SEALING WASHER BOTH INWARDLY INTO SEALING ENGAGEMENT WITH SAID THREADED SHANK AND FORWARDLY AGAINST THE COOPERATING WORKPIECE.