This is a Edge Tape Binder Attachment For Sewing Machines.

This binder folds the tape in half around the fabric and makes RAW finish top and bottom. It is used to insert Tape, Braid, or Binding along the edge of the garment as shown in the diagram.
This binder will fit most industrial and home sewing machines with attachment mounting holes in the machine bed including, Bernina, Brother, Consew, Gemsy, Juki, Mitsubishi, Rex, for SAILRITE, Singer, SunStar, Tacsew, Yamata and many more.