S. MAIL” – “P”. 2 1/2″ high x 1 3/4″ wide x 1 1/8″ deep. Stamped Brass body. Brass shackle. Pin tumbler. 3 pins.”P” than other stamped case locks. It was used by the Post Office for transferring accountable items such as stamps and money order blanks from the SDO (stamp distribution office) to associate offices. It was short lived and replaced with the regular registered mail lock.