Franz Meinke Reform Schloss: What makes this padlock unusual is that the key has cuts on the inside of the barrel. When the key is inserted into the lock the little nub on the outside of the key is pushed inward and this causes the cuts in the key to extend further into the key barrel and also into the lock's circular post or pin. This allows the key to turn fully clockwise and retract the locking bolt.
The patent describes it as follows: "These projections.... and the spaces between them correspond, when the key is turned in the lock, with the wards and the spaces between them of the key-pin.... secured in the lock casing as will be understood. A slot.... is formed in the corrugated key-pin or post.... for the reception of the bit.... on the insertion of the key into the lock and its withdrawn therefrom." The complete patent filing can be seen on Google.
The lock is patented under U.S. Patent Office #494,340. In addition to the name stamped on the padlock itself, both the key and the padlock are stamped "1" .