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A nickname for the stamps issued in 1930 for use in conjunction with the flights of the Graf Zeppelin and other rigid airships.
A type of grill used on the 1867 issue that measured about 11 x 14mm in size and with short horizontal ridges. The "Z" grill does not look like a "Z"; legend holds it that William L. Stevenson could not decide which family of grills the stamps belonged to and called it "Z."
(Zone Improvement Plan) First introduced in the late 1960s, this five-digit number facilitates the sorting of mail. The first three digits identify a major city post office, and the fourth and fifth digits identify the delivery area of a post office branch.