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 interlock

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 press the protrusions. Friction also plays a role, which can prevent two building blocks from sliding apart. The projection hole connection system uses the interference fit principle-the tight connection between two parts based on friction without other fasteners. You can make a 2x2 brick with three 2x2 boards or a 2x4 brick with three 2x4 boards. Alternatively, 2x4 bricks can be made of 2x2 bricks and wooden 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.