Horse-Tack Cast-Iron Buckle, Dug Locally

It had been inna ground long enough to have the appearance of a longish lump of iron-oxide, with just a hint of its present configuration discernible. I have managed to remove 95% of that red crust, leaving a surprisingly intact buckle. The question: how was it used in a harness? Are such items still used in working tack, or is this an obsolete artifact?

This has been logging territory for over 150 years, although we've over-harvested so badly that there's only a ghostly shadow of that once ubiquitous industry extant. Horses were extensively until after WWII, many of them large draft animals; Belgians, Clydesdale, an' etc.
Any observations an' comments are most welcome; thanks for lookin'!

 

I can't find a specific name for it, but I think it would have been used as a sort of quick connect for the cinch ring (the ring on the girth/belly band). The portion with the little post looks like what is called a "conway" buckle -

And the hook would receive the cinch ring.

This shows a modern version using a "tackaberry" buckle -