The gaps between the upper and lower floors are locked with each other, which makes the whole structure more firm and not easy to fall apart.

Plane interlocking

Stereo interlock

Most Lego bricks have two basic components-the upper protrusions and the inner holes. The bump of the building block is slightly larger than the distance between the hole and the side wall. When you squeeze the building blocks together, the protrusions will push the side walls outward and push the holes inward. This material is elastic and can keep its original shape, so the side walls and holes will squeeze the protrusions. Friction also plays a role, which prevents two building blocks from sliding apart. The projection hole joint system uses the principle of interference fit-the tight connection between two parts based on friction without other fasteners. You can use three 2x2 boards to make a 2x2 brick, or use three 2x4 boards to make a 2x4 brick. Alternatively, 2×4 bricks can be made of 2×2 bricks and boards at the same time. The colors of raw materials used in basic Lego components are blue, black, dark gray, green, light gray, red, yellow and white.