What I was thinking was a sleeve is actually the pipe that the flange is welded to. I took the whole thing off the car so I can actually see what I'm doing.
These won't even start into that flange on the cat. They fit easily onto the front pipe but are much too thick. It looks like something 1/8 in thick would be tight, but these are about a 1/4 or more.
I took some pictures in case mine is somehow different from how it should be.
