It looks like what my friend who is also a professional quilter uses for basting big quilts. The holes are to slide a bolt through to change the sizes of the square. In my experience you thumbtack a strip of heavy material to the boards and baste either with pins or thread your quilt to the strips of fabric on the frame. We had such a set up at our local Farm Museum. As the outside edges were done as far as the women could reach they rolled the board toward the middle and reattached it to the upright supports. It is possible for as many as 12 people to work on the quilt at a time if it is king or queen size.