Brass padlock developed by the Eagle Lock Company. The shackle front is marked “EAGLE LOCK CO.” The front body is marked "1000 / U. S. REG’D MAIL / PAT’D JULY 1871." The number 1000 may be the serial number applied to that lock. The end of the steel shackle has a notch in each side that engages with the six levers in the body. The Post Office Department used brass locks to secure registered mailbags as well as on “through” mailbags (“through mail” was only opened at distributing post offices) that were carried by mail contractors.