The stool's three hinged legs fit perfectly into a y-shaped hole in the seat, locking them into place.
This fit tightens when weight is added to the top, increasing the stool's stability.
The following text is provided by the designer:
An occasional stool that folds away neatly and easily with minimal components.
It folds away by picking up one side of the seat. Gravity, along with the angles used, enables the stool to fold out when put back down. The angle on top of the legs has been designed to add maximum strength. As weight is placed on the seat it pinches the top of the legs together creating a stronger join, the heavier the load the stronger the stool.