Circular mortise hinge

Claim 1

MEANS MOUNTING A PASSAGE DOOR IN A WALL OPENING IN A BUILDING, SAID MEANS COMPRISING AT LEAST TWO BUTT HINGES MOUNTED BETWEEN A VERTICAL EDGE OF THE DOOR AND A JAMB SURFACE OF ONE SIDE OF THE WALL OPENING, EACH HINGE BEING COMPRISED OF A PAIR OF CIRCULAR LEAVES, INTERFITTING KNUCKLES ON SIDES OF SAID LEAVES PROVIDING A HINGE BARREL, A PIN RECEIVED WITHIN SAID BARREL, A SINGLE SCREW HOLE THROUGH THE DIAMETRIC CENTER OF EACH SAID LEAF, A CYLINDRICAL PILOT HOLE IN SAID DOOR AND SAID WALL OPENING OPPOSITE EACH SAID SCREW HOLE, CIRCULAR MORTISES AROUND SAID PILOT HOLES ADAPTED TO RECEIVE SAID CIRCULAR LEAVES THEREIN, ARCUATE EDGES OF SAID LEAVES ADJACENT SAID BARREL EXTENDING BEYOND CORRESPONDING CORNER EDGES OF SAID DOOR AND SAID JAMB SURFACE, A SCREW RECEIVED IN EACH SAID PILOT HOLE AND THREADEDLY ENGAGED IN THE OPPOSING PILOT HOLE, EACH SAID SCREW HAVING A CYLINDRICAL BODY OF SUBSTANTIALLY THE SAME DIAMETER AS THE PILOT HOLE IN WHICH IT IS ENGAGED, THE CONVOLUTIONS OF EACH SAID THREAD BEING SPACED AT ITS ROOT DIAMETER, AND THE INCLUDED ANGLE BETWEEN THREADS BEING SUBSTANTIALLY WITHIN THE RANGE OF 25* TO 35* TO FORM A SHARP OUTER EDGE.