Hinge unit for seat with adjustable back rest

Claim 1

A HINGE UNIT FOR A SEAT WITH A PIVOTABLY ADJUSTABLE AND LOCKABLE BACK REST HAVING TWO SIDES, COMPRISING TWO SETS OF HINGE MEMBERS ADAPTED TO BE SECURED TO THE TWO SIDES OF SAID SEAT AND OF SAID BACK REST AND FORMING TWO PARTS, A FIRST MEMBER OF EACH OF SAID SETS BEING SECURED TO ONE OF SAID PARTS AND A SECOND MEMBER BEING SECURED TO ANOTHER OF SAID PARTS, PIVOTING MEANS FOR CONNECTING SAID TWO MEMBERS OF EACH OF SAID SETS, SO AS TO BE ROTATABLE, BUT AXIALLY IMMOVABLE RELATIVE TO EACH OTHER, SAID PIVOTING MEANS OF BOTH OF SAID SETS EXTENDING COAXIALLY RELATIVE TO EACH OTHER, A FIRST LOCKING MEMBER RIGIDLY SECURED TO ONE OF SAID HINGE MEMBERS OF EACH OF SAID SETS FOR EACH SIDE OF SAID SEAT, A BOLT ROTATABLY MOUNTED IN THE OTHER OF SAID HINGE MEMBERS, SO AS TO BE AXIALLY IMMOVABLE THERETO AND HAVING COARSE SCREW THREADS, A SECOND LOCKING MEMBER THREADEDLY SECURED TO SAID BOLT, MEANS FOR CONNECTING SAID SECOND LOCKING MEMBER TO THE OTHER OF SAID HINGE MEMBERS, SO AS TO PERMIT SAID SECOND LOCKING MEMBER TO MOVE INDEPENDENTLY OF SAID OTHER OF SAID HINGE MEMBERS ALONG A PLANE EXTENDING THROUGH THE COMMOM AXIS OF SAID PIVOTING MEANS OF BOTH OF SAID SETS OF HINGE MEMBERS, WHEREBY SAID LOCKING MEMBERS OF EACH OF SAID SETS OF HINGE MEMBERS MAY BE ENGAGED WITH AND DISENGAGED FROM EACH OTHER RESPECTIVELY, AND MEANS FOR OPERATIVELY CONNECTING SAID LOCKING MEMBERS TO EACH OTHER.