Hank, those holes were in the brass plates before I started. I think they may have come from a big electric motor or some such...
Fred, I got along fine without it for abut 90 guns. Then when my plywood clamps were about finished, I decided to build it. It really does make the job a lot easier. I can hold it in the bench vise at practically any angle, and never too far away from the vise, so there's lots of support and no chatter. It's especially nice for getting a good polish on the inside of the bow and rail.