Lid and Base
From DT Online
This package consists of two near-identical halves - the only differences being that one is slightly bigger than the other so that it can serve as a lid.
The package is usually glued or stapled into shape with the single tab. The base of the box interlocks quite rigidly without need for any additional fastening, but does not close well enough to contain very small objects (e.g. grains of sand).