NGC 2017 silver eagle struck thru and retained finned rim reverse. The coin has a long, thin sliver of silver metal struck into its reverse, which is from this or more likely another coin's "finned rim." Also, the coin itself has a finned rim. The only example like this we have seen, with the piece of finning retained like this.
This coin also has a finned rim on its rim, and doubtless the press was striking coins at too high a pressure, causing the finning. Coins being ejected risk having the finning "shaved off" when they are ejected, which would leave behind a sliver of silver finning. A piece was struck into this coin's reverse.