The present invention relates to a wood board (1) for outdoor decking (8) use, which board has been sawn from lumber close to bark side of the lumber, with a thickness in the range from about 10 mm up to about 32 mm, the wood board (1) comprises a first side (2) and an opposing second side (4), the first side (2) can be arranged as an upper side of the wood board (1) and the second side (4) can be arranged as a lower side of the wood board (1), or vice versa, between the first side (2) and the second side (4) the board (1) has two opposite short sides (9, 11). The wood board (1) is provided with a convex first side (2) and a convex second side (4).

At each straight edge of a plywood section which is to be coupled to an adjacent plywood section, one half of a coupling structure is provided and the other half of the coupling structure is provided to the other plywood section which is to be coupled thereto. A system is provided which only requires a single set screw to hold elongated coupling halves together while absolutely preventing warpage or displacement of plywood sections with respect to one another. Thus, a ramp structure is incorporated into a recess which results in the vertical dimension of a tongue substantially matching the vertical dimension of the recess when the coupling halves are coupled together. The ramp structure best facilitates sliding the coupling halves into connection and a single set screw can be advanced to hold the coupling halves together with assurance that no warpage or misaligning will take place.