Abstract: A structure comprising two interlocking hollow semi-cylindrical elements, one of which is larger than and encloses the other, and formed respectively by stamping operations from the material of contiguous edge portions of two sheet metal plates, which structure prevents broadside separation of said plates while allowing free relative articulation through an angle of 180.degree., and producing a tight joint between said plates at each extremity of said articulation and being free of sharp edges when said hinge is either in closed or open position.