US #2518 F Rate Tulip Error - Imperforate horizontal pair

1991 Mint Imperforate Pair
When postage increased to 29¢, these non-denominated "F" stamps were pressed into service until denominated stamps could be printed. A small number of imperforate coil stamps were discovered by fortunate collectors during the short period of time these stamps were on sale. (#2518 imperf coil pair)