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Claim 1

IN A METAL WINDOW FRAME STRUCTURE COMPRISING A HEAD, A SILL, AND JAMBS CONNECTING SAID HEAD AND SILL, SAID HEAD, SILL AND JAMBS EACH COMPRISING A TUBULAR SECTION SHAPED FROM SHEET METAL, THE IMPROVEMENT COMPRISING (1) A GROOVE OF SUBSTANTIALLY UNIFORM TRANSVERSE CORSSSECTION RUNNING LONGITUDINALLY AND THROUGH THE LENGTH OF EACH TUBULAR SECTION COMPRISING SAID HEAD, SILL AND JAMBS UPON THE SIDE THEREOF FORMING THE EXTREME SIDE, BOTTOM AND TOP OUTER PERIMETER SURFACES OF SAID WINDOW FRAME STRUCTURE, SAID GROOVE THEREBY FORMING AN OUTER PERIHPERAL GROOVE VERTICALLY AND HORIZONTALLY AROUND SAID WINDOW FRAME STRUCTURE, SAID PERIPHERAL GROOVE BEING ADAPTED TO RECEIVE SAID RETAIN THEREIN A FLANGE IN EACH VERTICAL AND HORIZONTAL PORTION OF SAID PERIMETER SURFACE, AND SAID GROOVE HAVING A NARROW WIDTH IN THE MOUTH THEREFO AND A GREATER WIDTH IN THE DEEPER PORTION THEREOF, (2) FOUR SUPPORTING FLANGES OF FLAT, THIN METAL, SAID FLANGES BEING POSITIONED RESPECTIVELY WITH A LATERAL CURVED PORTION THEREOF IN SAID PERIPHERAL GROOVE IN THE TWO VERTICAL AND TWO HORIZONTAL SURFACES OF SAID OUTER PERIMETER SURFACE, THE LATERAL CURVED PORTION OF EACH OF SAID FLANGES WHICH IS INSERTED IN SAID GROOVES BEING FOLDED SO AS TO PREVENT SAID FLANGES FROM MOVING LATERALLY OUT OF AND AWAY FROM SAID GROOVES, AND SAID FLANGES BEING ADAPTED TO BEING MOVED TO AT LEAST TWO POSITIONS WITH RESPECT TO THE PERIMETER SURFACE IN WHICH THEY ARE MAINTAINED, IN ONE POSITION SAID FLANGES LYING FLAT AND SUBSTANTIALLY PARALLEL WITH SAID PERIMETER SURFACE AND IN ANOTHER POSITION LYING IN A PLANE PERPENDICULAR TO SAID PERIMETER SURFACE, SAID FLANGES COMPRISING THE SOLE FLANGE MEANS FOR HOLDING AND SUPPORTING SAID WINDOW FRAME STRUCTURE WHEN INSTALLED SAID GROOVE BEING BUILD UP ON THE EXTERIOR OF SAID PERIMETER SURFACE OF SAID HEAD, SILL AND JAMBS BY A LONGITUDINAL FLANGE EXTENDING OUTWARDLY FROM SAID PERIMETER SURFACE AND RUNNING THE LENGTH OF SAID HEAD, SILL AND JAMBS, THE OUTER EDGE OF SAID EXTENDED FLANGE BEING TILTED TOWARD SAID PERIMETER SURFACE TO PROVIDE A NARROW LINEAR SPACE THEREBETWEEN WHICH IS WIDER THAN THE THICKNESS OF THE FLAT PORTION OF SAID SUPPORTING FLANGES BUT NOT WIDE ENOUGH TO PERMIT PASSAGE OF THE FOLDED PORTION OF SAID FLANGES, SAID DEEPER PORTIONS OF SAID GROOVE COMPRISING THE SPACE EMBRACED BY AND BETWEEN SAID EXTENDED FLANGE AND SAID PERIMETER SURFACE, SAID GROOVE BEING ADPATED TO RECEIVE THE FOLDED PORTION OF ONE OF SAID SUPPORTING FLANGES IN SAID DEEPER PORTION OF SAID GROOVE.