A machine or machine section (12) for squaring folded container blanks has a conveyor (16)for conveying slotted and partially folded container blanks (130). A folding device (34) completes folding of each con­tainer blank while being conveyed by the conveyor (16). A gauge plate (44) is inserted in a slot (142) in each of the slotted and partially folded container blanks (130). A mechanism (38, 46) moves the gauge plate (44) in timed sequence with the conveyor (16), inserts the gauge plate in the slot (142) before completion of folding of the respective blank (130) in order to "square" the folded blank, and then withdraws the gauge plate (44) from the slot. Overlapping flaps (132, 138) of each folded blank may be tacked together during "squaring" by drops of hot melt adhesive (140) which subsequently hold the flat folded blanks (124) square while the conventional slow drying water soluble glue dries. The "squaring" arrangement may be incorporated in a conventional gluer/folder machine.