This is a lens cap for a telelvision camera lens used by they Apollo 17 crew. The Apollo 17 astronauts used the TV camera during the last trip to the Moon. With the lens attached to their Westinghouse color television camera and connected by a cable to the spacecraft, mission after Apollo 11 could broadcast live color television images from the Moon.
This lens cap was transferred from NASA to the Museum in 1984.
This object is on display in James S. McDonnell Space Hangar at the Steven F. Udvar-Hazy Center in Chantilly, VA.