It is an opening system, in which a door leaf is divided into two asymmetrical parts. When opening the door, its parts fold and move to one side. At the top of a doorway the "Book T2" mechanism is hidden, which provides a smooth opening of the door. From the X-Series, the system applies only to models 7X.
ANIMATION OF THE “BOOK" SYSTEM
SERIES OF DOORS, TO WHICH THE "BOOK" SYSTEM CAN BE APPLIED