Originally Posted by cyccommute

I'm not saying that it should have been obvious to you. If you have seen these headsets before, they are immediately recognizable. They are a weird design and I was never sure why they were used. It's a belt, suspenders, duck tape, staples approach to headsets. The lock nut and the threaded cup are all that are necessary but, for some obscure reason, the middle ring was added. It's a dumb design.

The anti-rotation washers often turn on their own and get jammed in the threads. They are buggers to get off. Been there, done that.