Exceptional, thank you very much. To all who responded and your research. Highly appreciated.Your find is one of many components of "Draft Harness" horsegear. In this case the word Draft refers to pulling a buggy or wagon, not to saddlery for riding a horse.
I cannot recall the specific name for the component you found. It is the top section of the Girth-Band, shown in one of the drawings below. Some of the other photos show the iron skeleton of an excavated one, INCLUDING the odd "hook" seen on the top of your find. The one in those photos is from a US Army draft-harness, but there were also many Civilian versions -- such as the example shown in a (color) photo of a buggy-harness on the horse.