Plate block
a block of stamps from the edge of the sheet which shows the plate or cylinder that the stamps were printed from
A plate block is a block of postage stamps that includes the part of the sheet margin with the serial number of the printing plate(s) used to print the stamps.
Sometimes the plate numbers appear in the stamps themselves, but the more common practice is to include the number in the margin of each sheet, frequently alongside the name of the printer.
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