This is the first of three derailleur patents filed by the ‘Perm Machinery Factory named for the October Revolution’ in Perm, Russia. These patents have some notable features:
This particular patent features a rather odd parallelogram spring arrangement using a flat strip of spring steel formed into the shape of the letter ‘S’.
As an aside, the derailleur in this collection that I have called Kharkov 4th style shares the first two of the ‘notable features’ listed above. It also features Gian Robert’s idiosyncratic (and possibly expensive) twin parallelogram spring design - that could be seen as the inspiration for the third ‘notable feature’. Finally it sports a logo that could be seen as В for Велта (Velta) - a brand used by Perm. However I have only ever seen this derailleur fitted on Kharkov bikes and featured in Kharkov literature - so I will continue to consider it a Kharkov product - at least for now.