THat is clever, but I think there is an easier way. I use a large adjustable wrench on this. Just clamp it down on the derailler and tweak the handle. It gives great leverage, and is fast easy and fairly precise. THe longer the handle the better, and no fear of damaging the threads. If it's just a little bent I don't even take off the derailler, just grab the derailler with my bare hand just below the hanger and give it a little tweak.

On Oct 23, 2012, at 9:21 AM, Andrew Burnell wrote:

5. If you have a bent derailleur hanger, find an old, worthless hub axle with the same thread pitch, thread it into the hanger, and use as a lever to bend it back. Be careful not to strip threads or snap the hanger.