Clockwerk tail feathers

The Clockwerk Tail Feathers were some of the Clockwerk Parts that helped Clockwerk survive for hundreds of years.

History
Clockwerk replaced his organic tail feathers with robotic ones to prevent himself from aging.

Sly Cooper and the Thievius Raccoonus
Sly shot rockets into many of Clockwerk's external body parts during their boss fight, including the tail feathers.

Sly 2: Band of Thieves
In Sly 2: Band of Thieves, Dimitri used them in the basement of his nightclub as printing plates for his Parisian counterfeiting operation. Because of the rare alloy they were made of, the Tail Feathers would have never worn out, allowing Dimitri to print money forever.

Sly and the gang took out Dimitri and stole the feathers, effectively shutting down the business. They were later stolen back by Jean Bison and given to Arpeggio, and reassembled into the body of Clockwerk and then Clock-La. They eventually faded into dust when Carmelita destroyed the Hate Chip.

Trivia

 * The Clockwerk Tail Feathers seem quite large when Sly holds them up, but in the cutscene following Dimitri's boss battle, they are pictured as smaller and Sly is able to hold them in one hand. They are also colored a golden-yellow.