Tom,
If you pull up WATCHMAKING, REPLACING A GLASHUTTER BALANCE STAFF by Steffen Pahlow on Youtube, you can see the small fish shaped driving dogs and how they are used. Their purpose is to provide power to the part from the headstock of the lathe when turning between centers. Bob also covers this in one of his lessons but for a larger clock size part. It is the same concept but the Steffen Pahlow video demonstrates the procedure for a watch size part.
david
