This was a key for a lock that could be re-keyed by changing the order of the parts inside the lock. I didn't think the key was that rare, but given the final price I guess I was wrong.
This key had a high bid of $1,359.99 (Plus $3.62 Shipping).Curious old brass and steel key that can be reconfigured. The end unscrews and the fins can be interchanged. It measures 6 1/8 inches long. There is light wear and some tarnish. - eBay (15 Sept 2013)