The John Hancock pen was an early cartridge filling fountain pen. The cartridge is soft thin copper, and screws onto the section. A hollow extension of the inner section pierces a soft metal plug on the cartridge, opening it for ink to flow. The visible portion of the section is part of the barrel. Do not try to remove the section!. There is a pin locking the inner section to the barrel/section to prevent rotation of them due to screwing on a new cartridge. The patent was issued in 1923. These typically have a green ring between the blind cap and the barrel, although red is sometimes seen. Pictured is a standard size, about 5 5/8″. Two smaller sizes were also made.
Single piece barrel and outer section 
Fully disassembled John Hancock pen
