Full postmark and red numeral 5 rate mark on this stampless folded letter from D. B. Clarke to Philadelphia. No content in letter. Joseph Oat Corporation (originally Joseph Oat and Sons) is the oldest continuously operating industrial fabrication business in the United States. Founded in 1788 in historic Philadelphia, Pennsylvania, it was likely patronized by the U.S. founding fathers on their sojourns through narrow cobblestone streets. Started by Jesse Oat, the company sold copper works such as kettles and utensils, competing with other craftsmen including Paul Revere. Jesse’s son Joseph continued in his father’s footsteps adding brass and sheet-iron work to the product offering. Exquisite copper plates and lamps became the company’s forte. They also built stills, steam engine boilers, and pressure vessels for soda water bottlers. Ownership of Joseph Oat and Sons remained in the Oat family until the late 1800’s, when the business was sold to their accountant. In 1966, the business was acquired by its current owners, and the name changed to Joseph Oat Corporation. The business rapidly expanded and moved from its quaint 10,000 sq. ft. Philadelphia location to its current sprawling complex along the Delaware River in Camden, New Jersey. While there is no content in the folded letter, docketing indicates it was from D. B. Clarke, Washington.  Clarke was an author and created a tome on the architecture of Washington buildings.  Perhaps the original content had something to do with copper finishings Oat and Sons had provided to some of the buildings.