Siroco derailleurs have an unsprung sliding rod that is driven in an out by a pivoting lever. It's a simple, robust, effective mechanism - but is probably only good for two or at most three sprockets.

The rest of these derailleurs is competently executed but unexceptional.

Interestingly, Siroco derailleurs are covered by a couple of patents held by Antionette Vialette - one of a very small band of women who have held derailleur patents.

I believe that this is the later of my two Siroco derailleurs. In this example, the pivoting lever that is turned by a pulley driven by a looped cable arrangement. This is described in a 1942 patent.

• Derailleur brands: Siroco
• Country: France
• Date of introduction: 1942?
• Date of this example: unknown
• Model no.: unknown
• Weight: 225g excluding spring
• Maximum cog: unknown
• Total capacity: unknown
• Pulley centre to centre: 78mm
• Index compatibility: friction
• Chain width: 1/8”
• Logic: unsprung - so no logic!
• B pivot: none
• P pivot: sprung
• Materials: largely steel with a white metal main knuckle

Ref. 417