I bought four 3-door color boxes and used them to make two 6-door units. The screw holes were offset by about 1mm due to differences between the color boxes, so it was difficult to attach them. It took longer to attach the joint parts than it did to assemble the color boxes. In the end, I managed to attach them by adjusting the height by inserting cardboard underneath one of the color boxes. I think the difference between the reviews that say it was easy to attach and those that say it wasn't is down to the individual differences between the color boxes that were delivered. It's just luck. Once it's attached, it looks better and it's securely connected, so I'm very satisfied.