There is no national standard for bar codes used in book management. You can use code39 code, Kudba code or cross code 25 ... You can even write a bar code rule yourself-of course, you need to write a decoding program yourself.

Generally speaking, because code 39 can represent numbers and letters, it is very suitable for libraries.

Only numbers, numbers and letters, the length and width of printing can be decided by yourself-of course, the rules of bar code must be followed when printing.