There are feet for all sorts of esoteric (to me) things like quilting, embroidery, binding, sewing zips in, hemming and on and on; on each of those there should be the word SIMANCO and a number, if you google that you can identify exactly what it is and what it was for. In fact every single part made by Singer has this great feature, really very handy.........
Oh poo, I've just realised that yours is a Jones so the above is of no use to you at all, sorry; but have a look for a number, perhaps they had a similar system.....Or Bilmo is a Jones man, he may know.