dunster

It's a model 127, serial # allocated January 9, 1919, made in St. Jean, Quebec.

You start with this site:http://www.singerco.com/support/serial_numbers.html

Then click on the link for single letter (G), which gets you here:

http://www.singerco.com/support/serial_1letter.html

Then you look for the link for the G series, which gets you here:

http://www.singerco.com/pdf/SINGER_G_nos.pdf

And you find the bracket containing your number:

6640371 6665370 127 25000 January 9 1919 St. Jean, Québec

The 25000 means that 25000 numbers were allocated to that plant on that date for model 127's.