That is a piece off a Hope saddle or off the saddle blanket for the Hope saddle. I found one in West Texas last year. Here is a pic of the one I found along with the reference book and some pages from the book.
sweet I once found a partial pewter / lead sand cast "texas" star button made by a confederate picket post-- at a river fording area (shallow spot) along the st marys river (fla /ga border river) --it had a letter by each point of the star -- they must have ran short on lead as it only had 3 points of the star - t e x they must have left it because it was only a "partial" button not a full one