Abstract: The closure for one end of a cardboard box comprises flaps extending respectively from opposite sides (at that end) and bent toward each other so that one flap overlies the other. The outer one of these two flaps has a longitudinal slot. The inner flap is cut and bent longitudinally to define a tab which extends through that slot and lies against the outer face of the outer of these two flaps. A third flap extends from a third side at the closure end of the box and is bent down to overlie the first two mentioned flaps and tab. The third flap has a tongue which extends into the box along side the first mentioned two flaps and is lockingly engaged therewith.