Because I suspect some readers might be saying "Huh? That little ring-thing is a pocketwatch winding key?"... I'll answer more specifically. It is a broken one. The brass ring originally had a longer iron stem, which is the part which went into the watch and did the winding. When that part broke off, the watch winding key was discarded. That is why most ones we find a short, broken ones.
Here's a photo showing a similar variety of pocketwatch winding key. The version shown in in that photo has a solid disc at the center, instead of the ring seen on the (broken) one dug by FunWithTreasure. Others have a geometric shape (such as an Octagon) in the middle
I should also mention, key-winding pocketwatches are older than the "stemwinder" kind. Stemwinders didn't become commercially available until the 1850s. They very quickly became much more popular than key-winders because they eliminated the need for you to keep up with such a teeny-tiny key. So, the great majority of pocketwatch winding keys are older than the 1870s.