If you are plating, I think you will have to replace the collar. I don't believe you can have the dissimilar metals in the plating bath.
Bill, I believe it is a Dzus fastener, as they go back to the '30s.
"Invented and patented by an American engineer of Ukrainian descent William Dzus (Volodymyr Dzhus) in the early 1930s."
Richard L.