I haven't manged to detatch the threaded rod from the OTA. I suspect they are permanently attached or at least removing it requires signifcantly more disassembly of the OTA. I cannot see inside enough to see if it should unthread.
I'll have to retrieve my calipers from where they've disappeared and work out the specific details. Also talking to a few more people it seems a good approach would be going to a bolt and nut specialist with the nut from the rod and try to get a matching nut stronger than brass. or a cutter or Die kit ... new territory for me.
I'm not great with precision at such fine scale so won't attempt using a file myself, I think I'd likely do more damage
Thanks,
roger.