These are 21 Rene' 41 retainers that secured the Rene' 41 shingles on the outside of the Gemini VI capsule. The shingles protected the capsule from the tremendous heat generated during reentry into the Earth's atmosphere. Rene' 41 is made largely of nickel, chromium, cobalt, and molybdenum. Carrying astronauts Walter M. Schirra and Thomas P. Stafford, Gemini VI was launched on December 15, 1965 on a two-day flight. It achieved the first space rendezvous ever with Gemini VII. These retainers were removed from the capsule after the flight. Their manufacturer is unknown. NASA transferred them 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.