The later Duopars did away with locknut in a clever way. The newer attatching bolt is split perpendicular to the threads. The bolt is hollow and threaded on the inside. There's a little allen screw that threads into the attaching bolt in the back. When the allen screw tightens it forces the split threaded section to expand and locks the attaching bolt in place. The allen screw is flush with the inside of the hanger so there are no clearence problems. Perhaps you can find one of these. I suspect there are unusable Duopars out there because they bend easily (never back up with the derailleur not perfectly aligned the chain}, but they're too cool to thow away. I hope this is coherent; it's past my bed time.
Leonard Bulger Ann Arbor, MI
Tom said: I'm mounting a fairly clean Eco Duopar on a bike and running into a problem. The nut that goes on the back of the attachment bolt behind the drop out won't clear the chain on the small cog. I've used the nut before on a five speed set up, but this is a 7 speed ultra freewheel and things are pretty tight. On the other hand, the main bolt is holding the whole derailleur pretty tight to the drop out and the derailleur seems unmoving as I shift up and down the cluster.
Is this nut essential? Maybe it's only for simplex style drop outs without the stop/shoulder? Anyone else seen this problem?
Tom (Ten Thumbs) Adams, Shrewsbury NJ