I just don't know. I was making an observation about the belt in relationship to the hand wheel. According to ISMACS (note: this is an acroynym) and maybe needlebar seem to indicate that the Improved Manufacturing would be larger. I think there were some crossovers at least by 1908 that some 15 class machines were used in manufacturing. I also found a 16K class machine that was smaller, but was a chain stitch.
I found the 1883 patent that includes the pressure regulator in the arm at
http://patentimages.storage.googleap...s/US274359.pdf
According to my notes,
https://www.sil.si.edu/DigitalCollec...1775/index.htm was from 1884 I also found
https://www.sil.si.edu/DigitalCollec...2725/index.htm which is a parts list for Improved Family. The parts list for Improved Manufacturing from 1891 and 1893 can be found at
https://www.sil.si.edu/DigitalCollec.../NMAHTEX/1790/ and
https://www.sil.si.edu/DigitalCollec.../NMAHTEX/1791/
I haven't watched but maybe I think this might have some neat antique machines. Maybe do a search for Improved manufacturing??
https://www.youtube.com/channel/UCsO...BGDivcuQ3iOQBQ
Does your machine have the Singer logo cast into the base of the machine?
It sure looks like a "5" instead of a "3" in the serial number.
Janey - Neat people never make the exciting discoveries I do.