Format
The federal stamp is presently issued in panes of 20 stamps. Originally, the stamps were issued in panes of 28, but because of a change in the printing method (and to make stamps easier to count) a 30 stamp format was adopted in 1959. In 2000, the format was again changed to the present sheet of 20. Beginning in 1998, a single self-adhesive stamp was issued. This stamp and surrounding backing is approximately the size of a dollar bill. Most states and foreign governments follow the federal format. Many states issue a 10 stamp pane for ease of handling and mailing to field offices.
Read more about this topic: Federal Duck Stamp