A sheet of material (40) suitable for bending along a bend line (42) to a predetermined angle, includes one planar segment on one side of the bend line, another planar segment on another side of the bend line, one displacement (46) extending in the thickness direction of the sheet of material from the one planar segment, and another displacement (46') extending in the thickness direction of the sheet of material from the another planar segment. The displacements are dimensioned and configured such that they engage one another during bending and limit the angular displacement of the one side relative to the another side. The sheet of material (40), having a plane-to- plane joint, includes a tongue (77) formed in one planar segment, a receiver (79) formed in another planar segment for longitudinally receiving the tongue, a latch protrusion (84) formed in the one planar segment, and a latch recess ((86) formed in the another planar segment. The receiver holds a lower surface of the one planar segment in close proximity with an upper surface of the another planar segment and transversely limits the planar segments. The latch protrusion and latch recess are self-latching upon insertion of the tongu into the receiver.