I performed another search and, this time, I asked Google for images of "potter's tools." Nothing like your item came up, but this image
shows several tools with thick handles like the tool you have. The heftiness of the handle of your implement indicates to me that it has to be substantial because it might be used to exert great pressure or that it is used on/against a substance that is dense or resistant to impression. That could be clay.
Then, again, I could be totally off. Just another thought.