Of course, you are probably right, 'Nando. I was hoping that eBay piece might be legit, because as of now, it is the type of which I speak. My piece is similar, so could be a very old dumbell, but the jury is still out. Most dumbells were marked in some way, either on the individual balls or on the bar. These marks could include patent numbers, maker marks or weight size. Likewise, the old cast iron types, referred to among collectors of such as "circus strongman barbells" typically had..huh hum...huge balls with a very short bar between them just big enough for one hand. Likewise, frequently the bar itself would flair in the middle to allow a better grip.
Barshot had continued use all the way up until the American Civil War and it seems that by this point, the barshot (of the early/mid 19th) might have taken on more of the classic dumbell shape with rounded bar. That being said, this is my "thesis" only and still waiting for some concrete proof in the way of said examples. Anybody???