Antique Gold-Filled Chain With Key

The little key looks like it has been a real key to something because you can see turn marks on it. I don’t know what the metal is on key and I received the chain with key on it just exactly this way. The chain is gold-filled the markings has since worn off neat piece. The chain is almost 20 inches long without key plate see photos above for measurement of the key. Has wear which can be expected with antique items. When I got this it was a knotted mess but I untangled it and it looks quite lovely Reasonable offers are welcome on all my items