Abstract: A stackable cardboard box construction comprises a sheet of corrugated cardboard cut, grooved and folded to form a bottom panel, opposite side walls and opposite lengthwise walls united with the bottom by grooved fold lines. At each corner, the side walls and lengthwise walls have upwardly projecting tabs and are folded to form a hollow triangular column having double thickness walls and projecting up above the upper edges of the side walls and lengthwise walls. A triangular plastic cap fitting over the projecting upper end of each of the columns has a stop plane engaging the top of the respective column, a table spaced above the stop plane by reinforcing ribs and a frustoconical stud which projects up from the table and is received in an opening in the bottom of a next higher box in a stack to prevent side slipping.