These are variants on Singer's later model 15. The Japanese 15 clones have a few added features, a knob for the feed dog settings and a bit into the 50s some of them were given a stitch length lever with a new design, but with exactly the same mechanism behind. These machines used the same bobbin and bobbin case as a Singer 15. If you look up "15 clones" a long with search words like sewing machine and Japanese, occupied Japan, etc. you will find a lot of info. There's blog posts various places and there's a few threads on this forum. I don't think there are any records kept on the Japanese production, nothing like there are for Singer serial numbers.
As far as a I know they are all low shank and use the same attachments as Singer model 15 and 66.
Last edited by Mickey2; 12-29-2017 at 04:44 PM.