The screw at the back of the #2 foot makes me think quilting foot or hemmer foot. The screw would hold the bar.
Like a variation on this one:
http://www.sil.si.edu/DigitalCollect...ges/image6.htm
Top Left corner
Or this one:
http://www.sil.si.edu/DigitalCollect...ges/image5.htm
#83