Packing ring with anti-extrusion end rings

Claim 1

A PRESSURE-TIGHT JOINT BETWEEN TWO MEMBERS, THE MEMBERS HAVING SPACED, PARALLEL, CYLINDRICAL SURFACES, TWO SPACED ANNULAR SHOULDERS LOCATED BETWEEN THE CYLINDRICAL SURFACES, EACH SHOULDER BEING MOVABLE LONGITUDINALLY RELATIVE TO AT LEAST ONE OF THE CYLINDRICAL SURFACES, THE OPPOSING WALLS OF THE SHOULDERS BEING FLAT, PARALLEL AND PERPENDICULAR TO THE CYLINDRICAL SURFACES, THE SURFACES AND THE OPPOSING WALLS DEFINING AN ANNULAR SPACE; A PACKING ELEMENT IN THE ANNULAR SPACE COMPRISING AN ANNULAR BODY OF RUBBER-LIKE SEALING MATERIAL, AND AN ANTI-EXTRUSION ELEMENT OF RELATIVELY HARD MATERIAL ABUTTING EACH END OF THE BODY, EACH OF THE ANTI-EXTRUSION ELEMENTS COMPRISING A RELATIVELY THIN, IMPERFORATE, ONE-PIECE, SHEET-LIKE ANNULAR MEMBER HAVING INNER AND OUTER PERIPHERAL EDGE SURFACES, SAID MEMBER BEING FORMED WITH THE SHORTEST STRAIGHT LINE DISTANCE BETWEEN ITS INNER AND OTER PERIPHERAL EDGE SURFACES MEASURED ALONG A LINE EXTENDING RADIALLY FROM THE CENTER LINE OF THE ANNULAR MEMBER LESS THAN THE SHORTEST DISTANCE BETWEEN ITS INNER AND OUTER PERIPH-