Blind fastener

Claim 1

A BLIND FASTENER INCLUDING A CORE BOLT, A HEADED SLEEVE NUT AND A COLLAR ADAPTED TO BE DRAWN OVER THE SLEEVE BY THE CORE BOLT AND RADIALLY EXPANDED TO PROVIDE A SECOND CLAMPING SURFACE, SAID CORE BOLT HAVING A HEAD, A STRAIGHT UNTHREADED BODY SECTION ADJACENT THE HEAD, A THREADED SHANK PORTION INTERMEDIATE THE BODY AND AN END PORTION HAVING DRIVING SURFACES, THE MAXIMUM CROSS SECTIONAL DIMENSIONS OF THE END HAVING THE DRIVING SURFACES BEING NO GREATER THAN THE MINOR DIAMETER OF THE CORE BOLT THREADS AND THE MAJOR DIAMETER OF THE CORE BOLT THREADS BEING NO GREATER THAN THE DIAMETER OF THE BODY, THE CORE BOLT HEAD JOINING THE BODY AT AN ACUTE ANGLE TO FORM AN UNDERCUT DRIVING SHOULDER; THE HEAD OF SAID SLEEVE NUT BEING PROVIDED WITH DRIVING SURFACES AND SAID SLEEVE NUT HAVING A SHANK TERMINATING IN A TAPERED TIP END SECTION OF REDUCED EXTERNAL DIAMETER RELATIVE TO THE SHANK DIAMETER, AN AXIAL BORE EXTENDING THROUGH THE SLEEVE NUT, SAID BORE BEING PROVIDED INTERNAL THREADS ADAPTED TO RECEIVE THE THREADS OF THE CORE BOLT, THE PORTION OF THE BORE EXTENDING FROM THE TAPERED END TO A POINT WITHIN THE SLEEVE BEING PROVIDED WITH A COUNTER-BORE OF A LENGTH AND DIAMETER WHICH WILL PERMIT THE UNTHREADED CORE BOLT BODY SECTION TO BE RECEIVED THEREIN WITHOUT INTERFERENCE DURING THE DRAWING DOWN AND SEATING OF THE COLLAR, SAID END TAPER EFFECTING THE REDUCTION OF THE EXTERNAL DIAMETER OF THE SHANK IN A PLURALITY OF STAGES, THE INCLUDED CONE APEX ANGLE OF THE OUTERMOST STAGE BEING ABOUT 60* AND THE INCLUDED CONE APEX ANGLE OF THE INERMOST STAGE BEING ABOUT 30* AND WHERE THE INNERMOST AN OUTERMOST CONE ANGLES INTERSECT AT A POINT ABOUT MIDWAY BETWEEN THE SLEEVE WALLS; SAID COLLAR HAVING A STEEPED AXIAL BORE EXTENDING FROM END TO END, THE INTERNAL DIAMETER OF THE COLLAR BORE AT ONE END BEING SUCH AS TO PROVIDE A CLOSE TOLARANCED FIT FOR THE CORE BOLT BYDY AND THE INTERNAL DIAMETER OF THE COLLAR BORE AT THE OTHER END AND IN THE BARREL PORTION INTERMEDIATE THE COLLAR ENDS BEING COUNTERBORED TO A DIAMETER SLIGHTLY GREATER THAN THE EXTERNAL DIAMETER OF THE OUTERMOST PORTIONS OF THE TAPERED TIP OF THE SLEEVE NUT SHANK, THE COLLAR WALL THICKNESS IN THE BARREL BEING THINNER THAN THE WALL THICKNESS AT EITHER END, SUCH REDUCTION IN WALL THICKNESS BEING EFFECTED BY REDUCING THE EXTERNAL COLLAR DIAMETER IN THE BARREL PORTION BY ABOUT 15%, THE END OF THE COLLAR OPPOSITE THE COUNTERBORED END OF THE SLEEVE BEING CONED AT AN ANGLE COMPLEMENTARY TO THE ACUTE ANGLE AT WHICH THE CORE BOLT HEAD JOINS THE BODY; AND THE MAXIMUM EXTERNAL DIAMETERS OF THE CORE BOLT HEAD, THE COLLAR AND THE SHANK OF THE SLEEVE NUT BEING SUBSTANTIALLY THE SAME.