Planking construction

Claim 1

IN A STRUCTURAL ELEMENT IN THE NATURE OF A RELATIVELY LONG AND NARROW PLANK HAVING FRONT AND REAR FACES AND HAVING PARALLEL LONGITUDINAL EDGES, A KEY STRUCTURE COMPRISING TWO CYLINDRICAL WALL PORTIONS DEFINING PARTS OF A COMMON CYLINDER WALL PORTIONS DEFINING PARTS OF A SAID EDGES, SAID WALL PORTIONS BEING LOCATED ON OPPOSITE SIDES OF AND CONCENTRIC WITH A LONGITUDINAL AXIS, BOTH SUCH WALL PORTIONS PROJECTING REARWARDLY WITH RESPECT TO SAID REAR FACE, A GENERALLY CYLINDRICAL GROOVE-DEFINING PORTION EXTENDING ALONG AND PARALLEL TO THE OTHER EDGE AND HAVING A SLOT WHICH OPENS INTO THE GROOVE FROM THE GENERAL DIRECTION OF THE FRONT FACE, SAID GROOVE HAVING AN INTERNAL DIAMETER WHICH CORRESPONDS TO THE EFFECTIVE EXTERNAL DIAMETER OF THE CYLINDER DEFINED BY SAID WALL PORTIONS OF THE KEY STRUCTURE, THE DIAMETER OF THE KEY STRUCTURE AND GROOVE EXCEEDING THE WIDTH OF SAID SLOT, A LONGITUDINALLY EXTENDING REAR PORTION OF THE KEY STRUCTURE BEING RELIEVED TO REDUCE THE FRONT-TO-REAR DIMENSION OF THE KEY STRUCTURE SUFFICIENTLY TO PERMIT THE KEY STRUCTURE TO BE INSERTED THROUGH THE CORRESPONDING SLOT OF ANOTHER SIMILAR PLANK ELEMENT AND INTO THE GROOVE OF THE LATTER WHEN THE EDGES OF THE TWO ELEMENTS ARE BROUGHT TOGETHER WITH THEIR FACES LYING AT A SUBSTANTIAL ANGLE, WHEREBY THE TWO ELEMENTS MAY THEREAFTER BE ROCKED ABOUT SAID AXIS TOWARD SUBSTANTIALLY COPLANAR RELATION AND THEIR RESPECTIVE INTERFITTED KEY STRUCTURE AND GROOVE-DEFINING PORTIONS ARE THEN EFFECTIVE TO TRANSMIT STRESSES FROM ONE TO ANOTHER OF SAID ELEMENTS AT ALL ANGLES TO SAID AXIS, AND MEANS SPACED FROM THE RELIEVED PORTION OF SAID KEY STRUCTURE COMMUNICATING WITH EACH OF SAID PLANK ELEMENTS FOR EFFEDTING A SEAL THEREBETWEEN.