Boards are joined together with tongues and grooves, as cladding or sheathing for walls, roofs or floors. Every other board has tongues on both sides, and intervening ones have grooves on both sides. The latter are fastened by metal loop shackles, incorporating a flat piece fixable to the underlay, as long as the grooved boards are wide. At each end of the loops there is a bent shank to embrace the appropriate bottom groove shoulder. No nailing is involved, and boards can be prefabricated, and undergo some deformation in mounting.
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