I had to pack my bike (our folding tandem to be precise) for airline travel. I read up on how to do this and there was the recommendation to remove the rear derailleur, which I found plausible.

Removing it and packing it in bubble wrap and tapping it to a safe location on the inside was all very easy.

When I tried to re-attach the derailleur however (at the beginning of vacations! On a Sunday!) the bolt did not catch the thread correctly and stopped. After a few tries I started seeing filings in the thread in the hanger, so I stopped. I had done this once before as a dress rehearsal with no problem, but now I have one. I'll have to take it to a mechanic tomorrow when the shops are open.

In the meantime I'd like to know what i did wrong. Any ideas? Part of the problem seems to me is the fact that it is very difficult to see the bolt being directed correctly when the thread starts catching because so many objects obstruct the view. Any tricks?

I am also disappointed that nobody in any web site I consulted put a warning about this into the bike-packing instructions. I start suspecting that taking the risk of damage to the derailleur during transport (doesn't happen unless very careless handling occurs) is maybe smarter than taking the derailleur off.