In 1883 the "Improved Family" machine appeared and in 1885 the VS1 (Viberating Shuttle), in 1886 the 27 / 28 and in 1912 through the 1950's 128 / 128 were manufactured and sold.
BELOW YOU WILL FIND THREE TABLES THAT WILL HEPL YOU TO RESEARCH THE APPROXIMATE TIME PERIOD YOUR SINGER MACHINE WAS MANUFACTURED BY USING THE SERIAL NUMBER OR SERIES LETTER DESIGNATION.
The factory designation, if it was not made in the USA, followed the model number. There are other examples for the plants in Scotland and in Germany.Whether it was given a designating letter I do not know. There were four different models of the featherweight the 221-1, 221K4, 221K5,and 221K7. That is the only model of FW that Singer made with the switch on the light housing, all the others have the switch on the bed of the machine.Another check you can make to determine which model you have is to check the model number of the motor (see the plate mounted on the motor).The friction surface on the underside of the guide grip holds the fabric taut and provides handles for moving the fabric.Set your machine for normal free-motion sewing according to your operators manual.