I'm not an expert and my terminology may not be correct, but it looks like an old leg vice. It would attach to a woodworkers work bench. It might date back to the 1800s. Not sure.
My thoughts as well, I am sure many of us will drive our survivors crazy when they go through our shops.Look at his feet, is it big enough to be a leg vise? I've never seen anyone use a spacer block, but I suppose it's feasible. If the hole goes all the way through the spacer isn't removable so it would be for a specific use, like maybe a board wider than the block.
Many things like this were adapted by a craftsman for a specific task, like in a production shop.