This page is the starting place for identifying a machine cancellation on mail from the United States seen in the general period between 1900 and 1920.
Help is also suggested for cancels earlier or later than that time period.
Some of the information used here came from the Machine Cancel Society and other pointers to particular cancellations were derived from the very fine book Postmarks on Postcards by the late Richard W. Helbock.
I highly recommend Mr. Helbock’s book as a great starting-place for new cover and card collectors who want to learn more about postmarks. The book covers only the postcard era (1900-1920) in the United States. I urge you to purchase your own copy of the book. You can purchase it from these sources: “Postmarks on Postcards” from Amazon, or search on eBay for “Postmarks on Postcards” .
A very good overview of machine cancellations is available from The Machine Cancel Society in the form of an award-winning exhibit on the history of Boston machine cancels, by William Barlow, Jr. (recently updated) Viewing this exhibit is a great education in not only the evolution of machines in a major U. S. city, but also helps the reader to understand that these early cancels can sometimes be difficult to identify.
First, a quick nomenclature lesson:
Note that the “cancellation” or “killer” is the part that prevents the stamp from being reused. The “postmark” or “dial” is the part of the impression that tells you where the letter was mailed and when. Various machine dial designs were based on handstamps in use by U. S. post offices of the 19th century.
However, when machine cancel inventors approached the problem of cancelling the stamp, possibly at high speed, they used a great variety of designs.
(If you want, you can jump directly to the webpage with a list of machine cancel dials and killers. You pick your item from the page, based on the design, and will be sent to a page or pages that will guide you in the identification. Alternatively, you may follow the question-and-answer flow that follows.)
So, let’s get started. Keep the cover or card (or a photocopy) in front of you, and follow the information and links on this web page.