That would be perfection. Of course it would be ideal if we could own lathes and mill them to exact specification. That's not gonna happen in my case, so I hope someone can come on here and recommend a source that can supply any variety of ferrule we need. The last one I used was only a "make-do". It works, but the step-down bit as too small. My mechanic friend went through his whole collection for a perfect fit and the "make do" was all he could find. Everything else was too big.

I still have to try the metal valve cap bodge that is mentioned above. I need an odd sized step-down ferrule for a Sugino 75 derailleur.