Pretty worn and upside down in the picture. To me it looks like it is the slat from a farm elevator. They come in various sizes and are usually rectangular. I have never seen one as worn down as yours. If I was home I would run outside by the barn and post a picture of the whole elevator so you could see the whole chain with slats.
The rectangular chain link hooked to the slat is a type of chain that I have fixed many-a-time in the past. I cannot see from the picture, but there should be a slot in the link where the next link would fit in - kind of like the letter C in a side profile. You have to turn the links 90 degrees to each other to slide them together. That is so they do not come apart when they are aligned straight.
HH,
Scott (MI)