A toy-building element

A toy-building element for a toy-building system in which toy-building elements can be releasably coupled to one another using an interference fit between coupling studs of one toy-building element inserted in matching openings in another toy-building element, the toy-building element comprising:

• a body part with a top face, a bottom face and one or more flat sidewalls that extend around an outer periphery of the toy-building element,
• the one or more flat sidewalls at least partially define said interior of said toy-building element and the flat sidewalls extend between the top face and the bottom face with the sidewalls being connected to one another at right angles to form sharp corners,
• at least one cylindrical coupling stud extending at a given height from the top face, and
• at least one tubular projection extending inside the interior to the bottom face for forming at least one opening in the bottom face in which a coupling stud fits with said interference fit, said at least one projection being detached from said flat sidewalls,
• wherein said sides of said sidewalls facing the interior can be provided with contact ribs that extend from said bottom face towards said top face,
• characterized in that:
• the at least one tubular projection comprises four substantially flat contact walls extending perpendicularly to the bottom face, said four contact walls being arranged in a squared arrangement with each of the four contact walls arranged at a 45° angle with said side walls,
• said four contact walls of a tubular projection are connected to one another to form a tube with a squared cross-sectional outline, and in that
• a contact wall forms together with two sidewalls or with two contact ribs an opening in which a coupling stud fits with an interference fit with three contact lines and/or wherein a contact wall forms together with one sidewall or one contact rib and one contact wall of another tubular projection an opening in which a coupling stud fits with an interference fit with three contact lines.