The Code 39 character set includes the digits from 0 to 9, the letters from A to Z (upper case only), and the following symbols: space, minus (-), plus (+), period (.), dollar sign ($), slash (/), and percent (%). A special start/stop character is placed at the beginning and end of each barcode. The barcode can be of any length, although more than 25 characters are rarely used. Each character consists of 9 elements: 5 bars and 4 spaces. Each character includes 3 wide and 6 narrow elements. Characters are separated by an inter-character gap, which is the same width as a narrow bar.
Code 39 is widely used in many industries, and is the standard for a lot of government barcode specifications, including the U.S. Department of Defense.