I found these two items when going through some spare parts I received with the purchase of my 54 Manhattan. I have two of the chromed part (one in original K-F package which has a spring type backing plate included). I have about 6-8 of the nut -like item on the right, they are wrapped in a sort of waxed covering. The one in the photo was unwrapped and shows some rust.
I don't know what either item is used for but I am assuming they are K-F parts.