Here the image shows a lovely 66K about 1920, originally may have been hand, electric or treadle operated.It was manufactured between 1907 to 1920 the early machines were only Black and Gold with no colour.
While the majority of early 20th century, vintage Singer sewing machines are valuable as decorative items only, the early Singer models mentioned above still hold value as collectible antiques.
The good thing about restoring a Singer sewing machine is that the company is still around and replacement parts for antique Singer sewing machines are still available through the company.
Later versions 99K31 had a stitch length up-down lever with reverse stitch and numbered tension dial - Year 1955 The Singer 15K is always recognised by its tension unit being on the left face of the machine.
Its bobbin had to be inserted into a bobbin case, then the case was inserted into the machine vertically to the left of the needle.
An old sewing machine from any maker with a serial number of 5000 or less will have more value, especially those from obscure manufacturers.
Sewing machines with serial numbers above 50,000 would be considered later models had basically common.The Singer 15K was manufactured over many years from 1910 - 1964, then reproduced again in 1982 called the Singer 15N.The Singer 222K as shown has the sleeve arm or sometimes called tubular bed.I'm sure its still the smallest adult sewing machine ever produced.Its manufacturing year was 1955 to 1964 The Singer 66K is the large version of the Singer 99K.The sewing machine was an important advance in technology because it made mass production of clothing and textiles possible.