2 7/8″ high x 2 1/16″ wide x 7/16″ deep. Stamped Steel body. Steel shackle. Post key. “UNITED STATES MAIL LOCK PAT’D JAN 20.1891” is stamped on the obverse of the body. There are 2 stars stamped on the obverse of the case at 11 o’clock. “US” is stamped on the obverse of the key. Frank W. Mix Patent # 445121.