These bells are part of the harmonica and bell set carried by astronauts Walter "Wally" Schirra and Tom Stafford aboard Gemini 6 in December of 1965. The mission was to test the docking and maneuvering capability of the Gemini spacecraft.
Approximately five hours after the successful maneuvering of the the two spacecraft to within six inches of each other, astronauts Schirra and Stafford played "Jingle Bells" with these instruments and pretended to see a UFO called Santa Claus.
Astronaut Tom Stafford gave the bells and his harmonica to the National Collection in 1967.
This object is on display in Destination Moon at the National Air and Space Museum in Washington, DC.