Hi My Fellow TH'er
As this item is silver washed I do not think that it is horse tack. As Cudamark suggested it might well be off a serving piece, bowl or plate, etc. Can you tell what the base metal is under the silver? Congrats on the find. I hope that someone can give you an ID. ;-)
It may be half of a "T" type buckle.
Where the "T" part would fit up through the hole and turn and hold.
That would account for your wear marks...
Like the Tung and Wreath buckles.