Singer Class And Model Numbers
Full Singer model numbers took the form of say 15K80.
The first part (15) is a 'Class' number, which indicates the basic design of the mechanism.
The second part (K) is a location code for the factory where it was made. i.e. K = Kilbowie in Scotland, M = Monza in Italy, B = Bonnieres in France etc. The exception was Elizabethport, New Jersey which used a ‘–‘ symbol instead of a letter. A list of factories and their location codes can be found on the factories homepage.
The final part (80) was a sub-version number used to indicate optional features and/or changes over time.
Machines of the same sub-version are identical no matter where they were made, but those of different sub-versions have some different parts, even if made in the same factory. Thus a 15-80 is the same as 15K80 or 15J80 etc., but a 15K80 is not the same as a 15K81 or 15K91 etc.
This identification system is further complicated because it was common practice to abbreviate full model numbers to either just the Class number, or to the Class plus location code. The terms 15, 15K or 15K12 could all therefore be used for exactly the same machine.