Looks a lot like a weathervane globe often seen below the top mounted vanes. This would have been the swivel point for the wind to move the upper section. Usually a larger hole on the bottom and a smaller one on the top. Can't really see the top of yours there. Nice find you have there, here is one that I found a while back.
looking through the larger hole, it looks as if there is a smaller one but if you say there isn't one then it may be something else. another possibility then would be a finial from a bedpost or one from a flagstaff. But if no top hole then again maybe not.