This is the cap to a Zeiss lens used on the Contarex camera Ed White operated during his spacewalk on Gemini IV. The flown camera, considered U.S. Air Force property at the time of the flight, is in the collection of the National Museum of the United States Air Force in Dayton, Ohio. The camera and lens, attached to White's hand-held maneuvering unit when he performed the first spacewalk by an American, captured images looking back towards the spacecraft and mission commander James McDivitt.
NASA transferred this lens cap to the Museum in 1989.
This object is on display in James S. McDonnell Space Hangar at the Steven F. Udvar-Hazy Center in Chantilly, VA.