It is part of a pocketwatch winder. The part you'd grip with your fingertips is broken off. Not long after the American civil war, key-wound pocketwatches drastically fell out of public favor due to the advent of stem-winding watches (which eliminated the need to keep up with the tiny winding-key). That fact helps to time-date when your find was manufactured. But that fact does not mean that everybody threw away their key-winding watches after stem-winding was invented. Grandpa might have broken and thrown away his 50-yeer-old pocketwatch's winding-key in 1890.