I am trying to find out how to determine what I'll call 'sub-numbers' on the various singer models. I.E., 15-91, etc. I have my g'grandmother's restored singer table/case that I'm trying to find a machine for. I have the ismac's site but only get model 66 / 15 / etc. with no -##. When looking at - can't remember if it's the ismac or sandman site - as to which machines fit into which tables, it is very specific as to machine model. Can anyone tell me where I can get more specific model info or how to tell? Any help would be greatly appreciated.