Those are hand made, the ones we used on the log pond were one piece cast steel. You drive that into a log, and a chain with a toggle in the end passes through the hole, then the toggle opens up and that way one boom log is connected to another. When it's time to remove it from the log, you use your falling axe and hit the dog back and forth on the narrow side, then pull it out. Trust me, every now and then an axe ends up on the bottom of the pond. There are a number of reason for rafting groups of logs in a pond, and usually the boom logs just stay as boom logs and can be opened without driving the dog out of the log by using the toggle on the chain, unless the wind is blowing, then you can't get slack, and you can't log without slack. Friend of mine took a brand new axe out on the pond to open a raft, set the axe on the edge of the boat and lost the axe overboard. Years later the pond was drained, and we walked out there and he recovered the axe, and he has it at home now, using it, but he had to put a new handle on the head.
