I had some trouble getting my cabin heat muff to snug down onto the exhaust pipe. I could tighten the thing until I thought I was going to break the hose clamp and it would still be loose on the pipe.

There are two threaded rods that hold the end caps at the proper distance from each other and these also serve as a way to hold the two pieces of each end cap together. It turns out that the holes either were not in the right place or were just too small. Regardless, it was just enough of an interference to keep the end caps from tightening down on the exhaust pipe.

I took the thing apart and drilled the holes in the end caps out to #21 and rounded some of the edges of the end caps so they would fit together better and put it all back together. It worked like a charm. Now my cabin heat muff is solid.