Derailleurs do not get more confusing than this one. It is clearly branded 'Simplex', even using the correct logo. However, it adds the discreet subheading 'N. Arregui Eibar' - Nicholás de Arregui of Eibar in Spain went on to develop the Zeus brand. And the derailleur itself? Well it owes nothing to any Simplex design of the time, or any Zeus design of the following years, but it is highly derivative of a 1939 Super Champion Champion du Monde.

My best guess is that this derailleur was manufactured by Nicholás de Arregui in Eibar and sold under some kind of marketing license granted by Simplex. But why Simplex would sanction the use of their brand on what is clearly a competitor's design remains something of a mystery. Cue lots of blather about the 'fog of war'.

And, by the way, it's decently made with the overall effect spoiled slightly by the low-rent plating.

• Derailleur brands: Simplex but manufactured by the company that became Zeus
• Categories: Simplex - before 1945
• Country: Manufactured and 'designed' in Spain, with a brand from France
• Date of introduction: 1942?
• Date of this example: unknown
• Model no.: unknown
• Weight: 228g including hanger plate
• Maximum cog: 24 teeth? (from the equivalent Super Champion)
• Total capacity: 10 teeth? (from the equivalent Super Champion)
• Pulley centre to centre: not applicable
• Index compatibility: friction
• Chain width: 3/32" and 1/8”?
• Logic: low normal
• B pivot: sprung
• P pivot: none
• Materials: steel

Ref. 1681