This guy has had far too much time on his hands!!!! He has put together a website museum totally dedicated to the rear mech. Yes an AtoZ of all things rear derailleur, I bet you didn’t know there was so many to choose from? This is the bible of derailleurs for all you dedicated cycle mechanics, and altogether cycle geeks. Not only has he posted great photos, but found technical documents,Illustrations and some trivia on most of them. Have a look, I dare you, once you enter you won’t ever return. I reckon there is enough info here for a whole Cytech technical Two training module!!!