Polish Patent # 126,253 - Romet

Polish Patent 126,253 - Romet main image

This is an extraordinary derailleur design. There is no pivot in the rear knuckle (it is rigidly set in position), the parallelogram looks to be angled in the opposite direction to the one you would expect (and which everyone else uses) and the sci-fi style pulley cage plates would make Dan Dare proud.

Unfortunately I have never seen an example of this fine item - if, indeed, one ever existed.