Window and door structural element

Claim 1

A STRUCTURAL MEMBER FOR MAKING THE FRAME STRUCTURES OF CLOSURE MEMBERS SUCH AS WINDOWS AND DOORS, COMPRISING A TUBULAR METALLIC MEMBER OF RECTANGULAR SECTION, A UNITARY EXTRUDED TUBULAR SHEATHING OF SYNETHETIC THERMOPLASTIC MATERIAL COVERING SAID METALLIC MEMBER, SAID SHEATHING BEING PROVIDED WITH OPPOSED SIDE WALLS, OPPOSITELY EXTENDING RIBS ON SAID SHEATHING IN SUBSTANTIALLY THE SAME PLANE AS SAID SIDE WALLS, CERTAIN OF SAID RIBS BEING OF INCREASED WIDTH TO PROJECT A GREATER DISTANCE BEYOND SAID SIDE WALLS THAN OTHER OF SAID RIBS, RELATIVELY THIN SEALING RIBS FORMED ON THE OUTER ENDS OF SAID RIBS OF INCREASED WIDTH EXTENDING IN A DIRECTION OPPOSITE TO THE DIRECTION OF SAID RIB OF INCREASED WIDTH AND DIRECTED INWARDLY TOWARD THE SHEATHING, SAID RELATIVELY THIN RIBS BEING ADAPTED TO CONTACTUALLY ENGAGE ONE OF THE OTHER OF SAID OPPOSITELY EXTENDING RIBS ON AN ADJACENT STRUCTURAL MEMBER, SAID OTHER RIBS AND SAID RIBS OF INCREASED WIDTH OF ADJACENT STRUCTURAL MEMBERS BEING ADAPTED TO COOPERATE WHEN THE STRUCTURAL MEMBERS ARE USED FOR WINDOW AND WINDOW FRAME STRUCTURES TO FORM AN AIR CHAMBER ENCLOSED BY WALLS CONNECTING SAID SIDE WALLS AND THE INTERENGAGING RIBS, EACH OF SAID CERTAIN RIBS OF INCREASED WIDTH BEING PROVIDED ON A PORTION OF ITS FREE END WITH A SHARP EDGE WHICH PROJECTS AT AN OBTUSE ANGLE AND COOPERATES WITH THE ADJACENT SURFACE OF THE RELATIVELY THIN SEALING RIB TO FORM A LONGITUDINAL RECESS, WHEREBY WHEN A RIB OF INCREASED WIDTH IS ENGAGED BY ONE OF SAID OTHER OPPOSITELY EXTENDING RIBS OF AN ADJACENT STRUCTURAL MEMBER A SEALING SUCTION CHAMBER WILL BE FORMED IN SAID RECESS AND EFFECTIVELY SEAL THE JOINT THEREBETWEEN BY AN INSULATING AIR SPACE.