Utility is the most important factor in placing labels on the spines of books. They must last and be easy to read. With a proper card catalog in use, the call number on the spine will become the primary device used for locating a book on the shelf.
Labels are printed only as a four-piece set. One must be very careful in placing them because an error might require the reprinting of the entire set.
Because the spine labels are permanent, never place them on dust jackets. For the same reason, never put them over old labels which may not adhere as well. Leaving on old labels will confuse anyone looking for a book and also looks very sloppy. Remove all old labels before proceeding.
Since the spine labels are the most important factor in locating a book, them must appear on the spine if possible. Put the label on the lower left of the front of the book only if the printed number is wider than the spine. The white margins of the label can be wrapped around to the front and back.
It is very difficult to locate a book by call number when the spine labels are placed in various locations in the vicinity of the bottom of the book. They must be place at a uniform distance (about 1/4 inch) from the bottom so that the eyes can scan across the numbers easily.