shown at fig3 is still in the plane of its panel 22 and is to be bent in the direction shown by the curved arrow top closure panels 22 are now folded downwardly with their respective friction flaps 24 entering a space between first end panel 30 and third end panel 60 this space may be seen by the reference to the upper right hand portion of fig2 referring now to fig5 of the drawings the friction tabs 44 are again shown with each lying between a respective first end closure panel 30 and third end closure panel 60 again referring to fig4 it will be seen that stacking tabs 32 and 34 are arranged pair wise to thereby form four double thickness and upstanding stacking tabs tabs 32 are termed innermost stacking tabs while tabs 44 are termed outermost stacking tabs as may readily be visualized from fig4 and as clearly shown at fig5 locking tabs 70 and 72 are similarly pair wise arranged with each pair fitting into a respective portion of opening 53 this is shown perhaps most clearly at fig5 and it is seen that the distance between peripheral portion 52 of each opening 53 and an imaginary extension of fold line 50 is seen to be equal to three thicknesses of the sheet material i e of the corrugated paperboard as also clearly shown at fig5 openings 53 assist.