Plate block

What a plate block is

Printing plates and cylinders carry an identifying number that prints in the sheet margin. A block of stamps that keeps that margin, and therefore the number, is a plate block. Mystic Stamp Company defines it as a block of four or more stamps with the plate number in the margin. Specialists try to own a block for every known plate number of an issue.

How US plate blocks are sized

• Flat-plate issues: a 2 x 3 block (six stamps) from the middle of the top, bottom or side of the sheet.
• Rotary-press issues: a 2 x 2 block (four stamps) from a corner of the sheet.
• Multicolor printings added up to eight multi-digit numbers, so collectors needed many more stamps to keep a single plate block.
• Since December 10, 1980, a USPS release has defined a plate block as four stamps regardless of the number of inks.

Plate number coils

Coil stamps come in rolls, not sheets, so there is no margin. A plate number coil (PNC) is a US coil stamp with the plate number printed on the stamp itself, at regular intervals along the roll. The first was the 18¢ Flag of 1981. Collectors save them as strips of three (PNC3) or five (PNC5) with the numbered stamp in the center, and catalogs assign much higher premiums to PNC5 strips of earlier coil issues. The interval between numbered stamps has ranged from 7 to 52.

What plate blocks are worth

For most modern issues, a plate block is valued much like the stamps in it, and post-1940 US stamps generally trade near face value. The famous exception shows how far the format can go: the unique plate block of the Inverted Jenny, the block Mystic Stamp Company received for the 1¢ Z grill in 2005. If you have older plate blocks, keep them intact; breaking a block loses the plate number that collectors pay for.