[Problem] To Improve the appearance and reduce production costs of an assemblable structure, and further, facilitate assembly thereof, while permitting firm. assembly without using an adhesive. [Solution] A hard plate (1) configured from acrylic or the like is equipped with a first part that has a protrusion (2), and a second part that is provided with a recess (4) having an inner width smaller than the horizontal width of the protrusion (2). The maximum width (2w) of the protrusion is larger than the width (4w) of the recess. Slits (3) penetrating in the thickness direction are provided in the vicinity of the side surfaces of the protrusion (2), and the slits (3) allow the vicinity of the side surfaces of the protrusion (2) to be deflected. Alternatively, similar slits (40) are provided in the vicinity of the inside wall surface of the recess (4) so as to allow for pressing against the side surfaces of the protrusion (2).

The invention provides a modular modelling kit for drawing geometric structures using a handheld 3D printing pen, comprising construction modules (1), and is characterized in that each construction module (1) has a basically flat base (2) and at least one substantially vertical post (4) protruding from the base (2), having a contact point (4a).

A construction set assembly comprises a first construction element and a second construction element. The first construction element, which may be made of metal, may have a distal edge and a proximal recess adjacent to the distal edge, and the second construction element, which may be made of plastic, may have a wall and define a nest opening configured to receive the metal construction element. The wall may have an opening defining a cantilever member having a first end joined integral with the plastic construction element and a second end that is opposite to the first end and is unsupported and deflectable relative to an initial position of the cantilever member, with the second end having a hook protrusion protruding toward an interior of the nest opening.

Provided herein is a building block string accessory including a building block and a string. A first side of the building block is provided with a pair of mirror-symmetrical stringing structures that are spaced apart, each stringing structure having a stringing through-hole. The string includes two threading sections and two connecting sections, which are alternately arranged and interconnected to form a closed-loop structure. The threading sections are aligned with the stringing structures and are threaded through stringing through-holes of the stringing structures. A connecting member is provided between the two connecting sections, and the connecting member is detachably connected to the two connecting sections.