I had a good look at the buildable Transformer’s packaging, and they don’t have as much in common with the Hero Factory skeleton design as I thought. The Transformers design uses ball joints only where they are most needed to give the model free motion, such as the hands, shoulder, neck and feet. The remaining joints are more like a LEGO® Minifigure’s hand gripping a pipe. The size of the parts I could see suggest the ball joints are smaller than the standard seen in LEGO® models. .