I have a Standard (patented 1887) slim, but the bobbin case looks different. There is no tab on my bobbin case, just two cut out holes to pluck it out. I understand that there were variations to the Standard rotary machines, the 'newer' ones can do the chain stitch (with the right needle plates) pretty well. Mine is still shredding the threads in chain stitch mode.....still trying to figure out what went wrong. Oh but the lock stitch is just beautiful. I don't have the treadle base, so I am trying to put it on a normal Singer treadle base to see if I can still operate the machine with the right hinge holes (modified) on the table. Wish me luck!