Below are the official definitions and methods of precanceling as described in The Precancel Stamp Society’s Town and Type Catalog of the United States and Territories.
Definitions:
A precancel stamp, or precancel, is an adhesive postage stamp (or revenue stamp) that has been canceled, under proper authority, with a device designed solely for this purpose, before being affixed to mail (or taxable) matter. Postage stamps that have been canceled with parts of discarded precancel devices relegated to post canceling service are not precancels.
A precancel device is any handstamp, printing plate, arrangement of movable type, mimeograph stencil, or other implement designed to imprint the prescribed information (usually town and state) on each stamp before it is separated from adjacent stamps in sheet or coil form. That portion of the device that imprints this information once is called a subject; most devices consist of ten or more subjects, spaced to fit stamps of the regular issue current when the device was made.
A precancel type is an imprint clearly distinguishable from other imprints carrying this information. Usually each subject on a device shows the same type and, with few exceptions, each device furnished to a given post office, however applied, represents one type for that office. Variations in spelling, punctuation, or spacing on isolated individual subjects of a device do not constitute distinctive types, nor do variations in type face. If the date of use is included on each subject, changes in date do not create different types.
Device Procurement:
Devices for precanceling are procured in one of two ways:
Contracted Devices: Since 1913, various companies under contract to the U.S. Postal Service supply highly standardized devices ordered by the post offices throughout the United States. These devices are used by the Bureau of Engraving And Printing (Bureaus) or are used by the post office named on the device. (Contract Locals) The P.S.S. Official Style Chart deals with these contracted devices, and they appear as numbered types in this catalog.
Local Devices: Before mid-1913 individual post offices had local firms produce precanceling devices. After the introduction of standardized contract procedures and device specifications in mid-1913, under some circumstances, postmasters still chose to procure their precancel devices locally. These are considered non-contracted devices and are called “locals”. These devices appear with “L” prefixes in the PSS Town & Type catalog.
Methods of Precanceling:
Various methods are employed in applying the precanceling device to the postage stamps. The method chosen is usually a function of the number of stamps to be precanceled.
Contracted Devices
Bureau Prints: Used in post offices where a minimum of 250,000 precancels are needed. These precancels were prepared at the Bureau of Engraving And Printing for use in various cities. Sheet stamps were printed from plates containing 100 or 400 subjects, while coil stamps were printed from plates containing 170 or 432 subjects.
City-Type Coils: Used primarily in large cities where large numbers of precancels were required, but not enough to warrant a Bureau print. Special coil precanceling machines are supplied by the Post Office Department. These machines have used rubber, electroplate and steel devices. Few if any of these machines are still in use.
Electroplates: Used primarily in post offices requiring large quantities of precancels. Electroplates usually contain 100 subjects and are press applied to entire 100 stamp sheets. Such precancels are usually deep black in appearance and uniformly inked.
Rubber Handstamps: Used in post offices where small quantities of precancels are required. Usually constructed in 5 or 25 subject format, these devices are applied by hand resulting in wide variations in inking. Many of these devices show distortion with heavy usage. They were not supplied to post offices after 1932.
Stereo Handstamps: Used in post offices where small quantities of precancels are required. To replace rapidly wearing rubber handstamps, Stereotype metal handstamps were made available in 1932, and were provided to post offices until mid-1958. Initially prepared in 25 subject format but then changed to 10 subject, these devices were applied by hand, resulting in wide variations in inking, but usually darker and more uniform impressions than rubber handstamps.
Vinyl Handstamps: Used in post offices where small quantities of precancels are required. Vinyl materials were substituted for metal starting in mid-1958. Prepared in 10 subject format, these devices are hand applied and therefore produce variations in inking.
Local Devices:
Electroplates: Used primarily in post offices requiring large quantities of precancels. Electroplates usually contain 100 subjects and are press applied. Such precancels are usually deep black in appearance and uniformly inked.
Handstamps: Used in post offices where small quantities of precancels are required. Usually prepared in 10 or 25 subject format. These devices are hand applied resulting in wide variations in inking. Many of these devices show distortion with heavy usage.
Typesets: Used in post offices requiring large quantities of precancels. Like electroplates, they are press applied and are characterized by deep black impressions, uniformly inked.
Mimeograph: Used in post offices requiring modest quantities of precancels. A stencil is prepared on a typewriter and then placed in a mimeograph machine through which the stamps are passed. This form of precanceling usually produces a wide variety of line spacing and letter placement due to typewriter preparation. Usually dark black in appearance with slightly blurred impressions.
Integral Handstamps: In 1938 the Post Office Department ruled that precancels above the 6 cent denomination must carry the month and year as well as the users initials. Some firms used a device without the date and initials, applying these with a separate operation. Integrals include the initials, date and the precancel all in one device.
Integral Typesets: Same as the above except that the device is a typeset.