Ok. some more information and pictures!
Does it have any wear marks at all, like grooves or scratches, that may give a clue to how it was used?
Yes, on the side away from the metal, the wood appears more damaged than the top side, though whether this is just how it was made is hard to tell.
There's no obvious sign of wear on it, not even in the hole, but I hadn't noticed before that the metal ring is off centre, so the teeth are nearly flush with the wood on one side and sticking well out on the other side.
This seems very odd, as either the teeth perform a function which involves them sticking out away from the wood, or flush with the wood, but it's hard to imagine what function it could perform doing both.
The 2 nails go all the way through the wood, and have had the points flattened off, as you can see in the photo. This suggests that the ring had to be held very firmly in place to perform its job.
The item was on a table along side other very old and "rustic" looking tools such as saws, and other wooden tools.