Threepio's left leg (golden, prime universe)
vs.
Threepio's right leg (silver, also prime universe)
The left leg is original, straight from the factory, while the right one was salvaged from a CZ-3 bounty hunter droid that Space Jimmy Smitts fought off with his bare hands and crushed him in the airlock door. The leg and part of the pelvis was all that remained onboard.