Interleaved 2-of-5

The Interleaved 2-of-5 character set only contains the ten digits, 0-9. However, if you only need to encode numbers, Interleaved 2-of-5 does the job in about half the space of Code 39. Although much denser than Code 39, the theoretical data security of Interleaved 2-of-5 is not quite as high. For this reason, we suggest that Interleaved 2-of-5 always be used with the Check Digit option enabled or that you standardize on a single character length of Interleaved 2-of-5 barcodes.

The densest Interleaved 2-of-5 barcodes that can be printed on an Epson or IBM-compatible dot-matrix printer is about 9 characters per inch, not including the start and stop characters. On a laser printer, density can be increased to about 17 characters per inch. (For reading barcodes of this density, we recommend use of a high-resolution optical scanner.)

Each Interleaved 2-of-5 character is represented by five elements: five bars or five spaces. Like Code 39, the name Interleaved 2-of-5 comes from the patterns of bars and spaces that represent the individual characters within the barcode. Each character has two wide and three narrow elements. With Interleaved 2-of-5, characters are represented in pairs. In each 10 elements, the five bars represent one character and the five spaces in between them represent the next character.

All Interleaved 2-of-5 barcode messages must contain an even number of digits. Therefore, a leading zero will be added to the front of the Interleaved 2-of-5 barcode message in either of the following two situations:

• If the character message to be encoded contains an odd number of digits and check digits are not in use.

• If the character message to be encoded contains an even number of digits and check digits are in use.

Unlike Code 39, Interleaved 2-of-5 contains no intercharacter spaces. However, Interleaved 2-of-5 does have start and stop characters.

Unlike the Code 39 asterisk which is used as the start and stop character at each end of the barcode, the Interleaved 2-of-5 start and stop characters are different from each other. They are also shorter than the standard character length in the symbology and no particular character (like the asterisk in Code 39) is associated with them.

From left to right, the start character is:

narrow bar

narrow space

narrow bar

narrow space

From left to right, the stop character is:

fat bar

narrow space

narrow bar

Interleaved 2-of-5 barcodes can, optionally, include bearer bars either as a rectangular frame around the barcode or as two perpendicular bars across the top and bottom of the data-expressing bars.

The term "bearer bars" originates with the manufacture of metal grates: The bearer bars in a grate bear weight and run perpendicular to the trans bars (which connect the bearer bars).

When barcodes are printed directly on corrugated cardboard boxes, flexible rubber printing plates are used. These plates often bend when they make contact with the cardboard, resulting in a distorted barcode. To prevent this bending, box printers stiffen the plates by adding bars perpendicular to the data-expressing bars. A side-effect of stiffening the plates in this way is that the images of these additional bars are added to the printed barcode. By analogy with the bearer bars in metal grates, which  run perpendicular to the trans bars, the additional bars in the barcode have come to be called "bearer bars" as well.

A secondary purpose has been found for bearer bars: if a barcode reader passes over the barcode at too sharp an angle, there is a danger that it will not read data-expressing bars at the ends of the barcode. Since bearer bars can be used to prevent this, they are sometimes included even on barcodes that are being printed on a plain label with a label printer.