What is this? Anybody know. Is it a part from an enfield 303? It has a brass tubular body (about an inch and a half long,) two white metal screw caps. a small disk with four small holes in it is forced in place by a spring which is held by a pin (in this case improvised by a piece of wire. It has markings on the brass part. BB 54 (then an arrow pointing to the end with the pin) Mk 3 I found it at my fathers house this weekend. It was attached to the dog tags of a great uncle.