It's very simple. Books printed by block printing in ancient China are usually packed in thread, that is, the printed papers are arranged neatly, drilled out with needles, and then fixed with thread. This method should be regarded as a relatively simple and simple method, which was summed up by the ancients on the basis of practice and prevailed in Song, Wu, Ming and Qing Dynasties. Before the Tang Dynasty, scrolls and other methods were used. Later, the butterfly suit was invented, which gradually formed the thread-bound book now, and continued until the late Qing Dynasty. There are many terms in ancient thread-bound books, such as rare books, rare books, unique books and so on. These terms are determined by the quantity and quality of books. In ancient times, thread-bound books could be produced on a large scale, unlike the machine manufacturing now, which was done by craftsmen, although there was some division of labor.
The so-called paperback book is the book I read in my daily life now. This is machine printed. It used to be nail printing, but now there are many offset printing. One disadvantage of offset printing is that if the book is too thick, such as a dictionary, it is easy to page out. Therefore, thick books such as dictionaries are still packed in thread, which is of course more complicated.