The Benjamin Franklin Z Grill, or Z grill stamp from 1868 is one of the rarest and most valuable U.S. stamps, there are only two of the pieces. She has a par value of one cent and one of the most expensive stamps in the world.
In this and other U.S. postage stamps were minted as a security measure a Waffeleinpressung or grid (English grill ) to make it difficult to be used again. This stamp has a Z grid, based on the classification of the stamp grid according to William L. Stevenson.
A copy is in the New York Public Library under wraps. The second copy was sold to the then record price of 935,000 U.S. dollars to Donald Sundman 1998. In 2005, she traded Bill Gross against a block of four Inverted Jennies worth 3 million dollars of Sundman.