A part includes a fastening system for fastening to another part so as to form all or part of a ball game board, the part including a plurality of cavities arranged in a two-dimensional ordered array on a first surface of the part, each cavity being designed to receive a ball, the part including a device for reversible fastening to another similar part along a fastening border, wherein the fastening system is formed by a plurality of overhangs each including at least one cavity of the plurality of cavities; and a plurality of indentations designed to receive the overhangs from another similar part.