Plate number

A plate number is a number printed in the margin of a sheet or roll of postage stamps which shows the printing plate used to print the stamps.

A plate number is the serial number of a printing plate. It is printed in the selvage or border of a pane of postage stamps.

Philatelists and stamp collectors analyze or collect plate numbers and stamps with different plate numbers. The American Plate Number Single Society (APNSS) is an example of a specialist philatelic society which focuses on plate numbers. APNSS is affiliate #178 of the American Philatelic Society