A kind person on a vintage sewing machine board that I'm a member of came to my rescue by sending me the directions for this hemmer.
From the directions, studying the attachment, and playing with it, I was able to get the thing to work for me.
Note from person who sent the directions:
It is a Chain Stitch Hemmer. The only picture shows it with the hole to the right with the letter A inside and the scroll part is at the left aimed up. The instructions read as follows, without any picture of it attached to the machine:
This attachment is not fastened to the presser bar, but by a thumb screw through hole A to the screw hole in bed of machine at right of needle plate. The thumb screw for fastening will be found with accessories.
This hemmer turns the goods just the reverse from the ordinary hemmer --throwing the hem underneath instead of on top, and is therefore used where a chain stitch is desirable.
Draw the goods into the hemmer until the edge of goods is far enough advanced for needle to enter the hem, then letting down the presser foot, proceed to sew as with ordinary hemmer. See that the edge of goods is kept against inner side of scroll, so that sufficient material is turned in to form the hem. In finishing a hem, place tip of finger against side of scroll to hold goods in position in hemmer until entirely through.
For a fine narrow hem this hemmer is equally desirable for lock stitch work.
Photos of the process:
Hemmer properly attached to machine. There is a little lip to the hemmer which must be inserted into the small hole that looks like a keyhole. This helps holds the attachment into place along with screw on right. The lips job is to keep the hemmer from traveling into the foot as the machine pulls the fabric through when stitching.
I had to take the hemmer off the machine to feed the fabric through since it was impossible to feed the fabric through the tip of the gadget while on the machine.
This sweet machine stitches a very lovely chain stitch to make a wonderful hem.