This is an extendable handrail similar to those used by astronauts during Gemini program EVAs when the spacecraft rendezvoused with an Agena target vehicle. An astronaut performing an EVA would place one end in a hole in the target vehicle adapter and attach the other end to a fixture on the outside of the Gemini capsule. The handrail made it much easier for the astronaut to move from the capsule to the target vehicle and back. This handrail is marked "Not for Flight" and was probably used for training. Its manufacturer is unknown. NASA transferred the handrail to NASM in 1968.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.