Abstract: A building block system, in particular a toy building block system, comprises a plurality of inter-connectable building blocks (1), whereby each building block (1) comprises an undercut trough-shaped groove (3) on at least one lateral surface (2) into which a connection bar (5) with a cylindrical part (6)is insertable. The building block system is suited for a variety of uses, easy to handle and provides many form-locking connection options of one or several building blocks, including of building blocks of differing geometrical form. According to the invention, the connection bar (5) is also formed with a hammer head-shaped boundary body (7) on at least one end of the cylindrical part (6), which can be inserted into a corresponding recess (11) on the end of the groove (3) in the building block (1) so as to form-lock with the lateral surface (2) of the same, when the connection bar (5) snaps into the groove (3) of the building block (1).

Abstract: A plug-in module is described; one side of this incorporates four spring leaves (6, 6') that can be deflected slightly outwards and which are arranged on one side in a tulip shape and which, on the other five sides surfaces (2 to 5), can be snapped onto a similarly constructed plug-in module. The side surfaces incorporate ridges (8, 8') which can be either continuous or segmented. On their inner sides, the spring leaves are provided with corresponding connecting elements (7, 7', 7") which snap behind the ridges described above. The production of a connection between two plug-in modules is effected first by a slight outward deflection of the spring blades from their rest position and by them subsequently snapping into position behind the ridges described above. The plug-in modules entail the advantage that even after a long time and frequent use, they can still be connected to each other easily or released from each other with equal ease.

Abstract: In a wheel for use with a modular assembly system with plug-in-type elements, the dimensioning of all of the elements being based on a basic unit length a, the wheel having a square central axle hole with a cross-section of a.times.a, rectangular slots with a width a being radially cut into both of the laterial faces of the wheel and arranged in pairs axially opposite to each other, axial openings are provided in the areas of the slots to provide a connection between the axially opposed slots.

Abstract: For the production of panels of a toy construction set, a base element of rectangular shape is disclosed, which as at least two square openings a.times.a, and which constitutes a flat hollow body, which is open on one large rectangular surface. The distance of the openings from the outer surfaces of the base element is a/2. Preferably, the base element has at least eight openings, which are arranged in at least two rows which lie on top of each other in rectangular array, each row comprising at least four openings which are next to each other.

Abstract: A toy building block is disclosed which is in the approximate shape of an "A" formed by two legs fixed to an apex portion which includes a square socket opening. Building blocks of this shape are joinable by an axle inserted into the apex opening the axle having either a square or circular cross section, all of the dimensions of the building blocks and axle being based on a basic unit of length a.

Abstract: A toy-figure or doll is provided which is especially configured and dimensioned for use in conjunction with a modular, plug-in-type building-block system with H-shaped block modules according to U.S. Pat. No. 3,838,535 (German Pat. No. 2,161,913). This toy-figure comprises movable arms, hands, legs and head. All measurements of the toy-figure and its component parts are sensibly adapted to the modular system which is based on a basic length unit a inasmuch as, for example, the length, breadth and depth of the figure, shoulder height, distance between the hands, grip-opening of the hands etc. all amount to whole-number multiples or fractions of the basic length unit a.

Abstract: A wheel for use in a construction system of building bricks in the form of the letter "H". This system is based on an arbitrary standard dimension "a". The wheel has a rim and a hub and optionally a ring surrounding the rim. The wheel is provided with axially extending grooves. The specified dimensions make the wheel especially advantageous for use with the system.