We now proceed to measure for the tab that will tuck into the opposing flap and serve to keep the enclosure closed. The tab is square in shape. For books of average size, it is about 4 cm square. Its size can of course be adjusted, depending on the size of the book.

First, a mark is made 4 cm toward the outer edge of the flap from the center point. (Orientation is the same as in the previous image.)