When I got my older machine (401 Slant-o-matic) I spent the day to see if the bobbins (a large bag of them) fit the machine in accordance with the bobbin already in the case. It was obvious many did not fit the case. Those were cast aside. This machine I found out later was not the previous owner's only machine. She had 3 and a serger set up in her studio. She was an interior designer. Some of the bobbins go to the other machines I'm sure but don't know who has the other machines. Mine was the only one in the estate sale.