Bookshelves can be divided into metal bookshelves and wooden bookshelves according to materials, and metal bookshelves can also be divided into five types: single-column bookshelves, multi-column bookshelves, stacked bookshelves, compact bookshelves and sliding bookshelves. Single-column bookshelf is generally 900 mm in length and 2000mm； in height; ; Stacked bookshelves can maximize the use of available space, so libraries and other public places often use them. The size of stacked bookshelves varies from country to country. For example, the height of each bookshelf in the United States is about 2280 mm, while that in Britain is 2250 mm. ..