I went looking but couldn't find it. Maybe I should change to - "never let stuff you are looking for know you are looking..."
It is a thing that is a bit taller than the bobbin - I never experimented with that thing - the manual I have does not show a good pic of the BCase. That thing might be not even belong to the machine. I don't see any little arm that would make it chain. I guess that's why I never tried it. I just couldn't see how it would do anything.