Plate Block - in The United States

In The United States

Until the late 1960s, United States stamps included two rows of stamps attached to one another in a block of four or more, with printing information, including the printing plate number, on attached margin paper. A number is used to identify one specific plate or cylinder used to print the stamps.

Then plate block collecting changed in the US due to the addition of up to eight multi-digit numbers which represented different colors used to print the stamps. The numbers were printed along the selvage. This meant collectors needed many more stamps to save a single plate block. This lasted for about ten years before the post office reverted to the traditional single number for most stamps. In a press release dated Dec. 10, 1980, the postal service announced a new plate numbering system that would, except in cases where more than four designs appear on a pane, "establish a plate block as consisting of four stamps regardless of the number of inks used or the press used to print the stamps." Now, new issues often begin with a number such as "11111," with each digit in a different color. Stamps printed in large quantities may have multiple plate numbers so the next plate combination might be identified as "22222" and so on.