In U.S. philately, the duplex cancel is a well-documented handstamp device that combines a circular postmark (indicating the town and date) with an attached "killer" (typically an oval or "football"-shaped barred design) to deface the stamp and prevent reuse. The numeral within the killer bars has been a subject of interest among philatelists, and several authoritative sources provide insight into its meaning.

According to established philatelic literature, the numeral in the killer portion of a U.S. duplex cancel generally served as an identifier within a specific post office. It was not typically a code for the town or post office itself, as seen in some European systems, but rather a marker for internal use. The most widely accepted interpretation, supported by key references, is that the numeral often denoted the postal clerk, workstation, shift, or a specific canceling device used at that post office. This allowed postal authorities to track the processing of mail within larger offices or to distinguish between multiple canceling machines or clerks operating simultaneously.

One key reference is the work of Gilbert Barr, whose articles "Standard Hand Stamp Cancellations on the Bank Note Issues" were published in The American Philatelist from January 1935 to April 1936. Barr’s research, later reproduced by the U.S. Cancellation Club, details how numerals in duplex cancels were used to identify individual cancellers or clerks, particularly in busy urban post offices like New York City or Philadelphia. While his focus was on the Bank Note era (1870s–1890s), when duplex cancels became widespread, the principle carried forward into later periods.

Another authoritative source is the article "How to track down the killers on your stamps" by J.H. Krulla, published on Linn’s Stamp News (April 27, 2021). Krulla explains that in U.S. duplex cancels, first used in New York in 1875, the numeral at the center of the killer "identified the postal worker, shift, position or branch by which or where the cancel was used." He notes, however, that "with notable exceptions, the numbers or letters of cancellation devices used in the United States do not carry information that can be used to identify the place of origin," distinguishing U.S. practice from European coded obliterators.

The U.S. Cancellation Club, a specialized group within the American Philatelic Society, has also documented that numerals in duplex killers were often specific to the operational context of a given post office. For example, in large cities with multiple stations or branches, the numeral might indicate a particular station or clerk, though comprehensive records linking specific numbers to individuals or locations are rare and often lost to history.

An additional resource is the discussion on Stamporama ("Identifying US duplex cancels," January 16, 2014), where collectors note that numerals likely identified the canceller used by a clerk, but emphasize the lack of a universal key to decode them across all post offices. The consensus aligns with Barr and Krulla: the numeral’s meaning is tied to internal post office logistics rather than a geographic code.

In summary, based on these philatelic references:

The numeral within the killer bars of a U.S. duplex cancel typically represents an identifier for a postal clerk, workstation, shift, or specific canceling device within a post office.

Key sources include Gilbert Barr’s articles in The American Philatelist (1935–1936), J.H. Krulla’s article in Linn’s Stamp News (2021), and discussions from the U.S. Cancellation Club and Stamporama.

These references provide a solid foundation without speculation, though they acknowledge that precise identification of a numeral’s meaning often requires context from the specific post office’s records, which are not always available.

Roy











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