In the late 1930s Super-Inax produced a series of extremely strange derailleurs. These were single pulley models with the main arm underneath the chain and the pulley mounted in a freely rotating 'pulley cage' above it. The strangest part of the design was the b-pivot. This could not only rotate in the plain of the pivot, as you might expect. The main arm had a curved face at the b-pivot so that it could also swivel slightly perpendicluar to the pivot. The spring at the b-pivot not only provided chain tension, as convention demands, but also provided compression at the joint keeping the b-pivot naturally straight. The cable outer stop is offset at the b-pivot and the cable clamp bolt is on the main arm - so that as the cable is pulled, the main arm moves sideways.

I am aware of 4 types of these strange devices:

• I think that the first type is mainly bronze, mounts inside the dropout, has the cable inboard of the main arm, is top-normal and the main arm is straight.
• Then the mounting remains inside the dropout, but the cable was moved outboard of main arm making it low-normal and, consequently the main arm is now curved. You can see this version here.
• Then the mounting is moved outside the dropout - but the rest stays the same.
• Then the dropout mounting is changed from bronze to aluminium.

Finally I would note that these Super-Inax derailleurs share a number of distinctive small parts with the later and seminal JIC and Super-Inax parallelogram models. They all clearly come from the same factory.

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I think that this is an example of the third of the 4 types of Super-Inax's distinctive single pulley design, described above. It has the following features:

• It mounts on the outside of the dropout, with a bronze arm.
• The cable runs outboard of the main arm - making the derailleur low-normal.
• The main arm is curved.

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• Derailleur brands: Super-Inax
• Themes: Ultra-lightweight - single pulley models
• Country: France
• Date of introduction: 1939
• Date of this example: unknown
• Model no.: unknown
• Weight: 153g including hanger plate
• Maximum cog: unknown
• Total capacity: unknown
• Pulley centre to centre: not applicable
• Index compatibility: friction
• Chain width: 3/32” and 1/8”?
• Logic: low normal
• B pivot: sprung
• P pivot: unsprung
• Materials: largely bronze with steel pulley and pulley cage

Ref. 477