i replaced the muffler on my 71 911s with a dansk stainless steel sport (2 inlets one outlet) and since the nuts & bolts that attach it to the heat exchangers were very rusty i ordered new ones from a dealer. the bolts seem normal enough but ive never seen any nuts like these (#999.084.002.02). they appear to be copper and have a sleeve of sorts that extends from one side of them by about 3mm. there is a slit cut into the sleeve and then that gap is pinched closed. althought this sleeve is threaded along with the bolt its is not easy to thread the bolt through. i am surmising that this is some sort of funky locking nut with the sleeve side of the nut going on the end of the bolt.

does this seem right?