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:

• The first two have one adjustment screw on the centre line of each knuckle, in the style of a Gian Robert.
• All three use aluminium castings for the parallelogram plates (rather than the steel pressings more characterisitic of Kharkov designs of the period).
• They feature a parallelogram spring that is not attached to either knuckle but sits in the centre of the parallelgram, acting between the parallelogram plates.

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.

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• Publisher: Rospatent
• Inventor: Yuri Petrovich Potekhin, Valery P. Kartashev & Leonid I. Arhalovich
• Country: Russia
• Date: USSR application filed September 1979
• Derailleur brands: Perm
• Derailleurs: unknown