Union, ME, duplex handstamp
The Chambers shop in Lodge, Virginia, produced this duplex postmarker in 1904 for the Union, Maine, post office. It is representative of devices from that era. It has a thumb-screw for tightening date type within the center mortise. Later postmarkers required a key to turn the square-head set-screw. The change was made because the edge of the thumb screw occasionally projected beyond the edge of the postmark die's imprinting surface. Striking the handstamp would jar the edge of the thumb-screw. This either over-tightened the screw so that it was difficult to release type or loosened the screw so that type would slip out of face alignment.
This Union duplex postmarker is similar to another handstamp in NPM's collection from the same post office. That postmarker has the state name spelled out. In the early twentieth century there was no systematic procedure for how states were shown in postmarks, although over time agreed-upon abbreviations evolved.