United States Postage Meter Stamp Catalog/Meter and Permit numbers
Meter and Permit Numbers
All early meter stamps showed both the permit number and the manufacturer's meter number. After 9 May 1929, the permit number was no longer required if the stamp included the meter number. Meter stamps showing a permit number have not been used in decades.
The meter number identities the actual postage meter machine. Meter numbers often have a letter prefix that identities the meter manufacturer. Meter numbers generally run in series. The series often identifies the meter model. The meter number does not necessarily change when the stamp design changes. Different meter stamp design types are known with the same meter number generated before and after the print head was changed.