Huret Dural Competition (3rd style) derailleur

This Huret derailleur is often referred to as the Huret Aluvac as it has the word ‘Aluvac’ cast into the back of the main arm. The real name, with which André Huret blessed it, is the Huret Dural Competition. I suspect that Aluvac refers to some kind of vacuum casting of aluminium used in its manufacture.

Despite being manufactured in wartime France, it is a handsome item with spectacular build quality. It is light, it feels reassuringly strong, the castings are precise, the nuts and bolts are beautifully machined, the movement is smooth and free of play and even the paint seems to be inclined to stay attached to the metal. Would it be inappropriate to suggest that it feels more German than French?

The Huret Dural Competition is a simple direct pull device, with the outer cable stop just below the bottom end of the spring and the cable clamp bolt on the pulley cage plate. It is also a single pulley design with all that implies in terms of total uselessness. However in addition to the build quality it has a certain style and cleverness. I particularly like the flowing curves.

I believe that there are at least 4 different variants of the Huret Dural Competition:

The first variant (1942) has a steel hanger plate, pulley cage plates that are restrained in shape but subtly dished and, crucially, no volute spring covering the sliding cylinder.
The second variant (1943?) introduced more extravagantly shaped but flat pulley cage plates, a volute spring to protect the sliding cylinder and has the top of the tension spring held by an arm that can be moved by a cable to detension the gear. It was possibly introduced as a 'detension' option to run alongside the first variant.
The third variant (1944?)is an update of the first variant with restrained but flat pulley cage plates, an aluminium hanger plate, a volute spring and no 'detension' system.
The fourth variant (also 1944?) is a 'detension' version of the third variant, possibly to run alongside it.

The first and third variants (both of which had no 'detension' system) appear to have a main arm with a shiny silver plated finish. The second and fourth variants (both of which have a 'detension' system) seem to have a main arm with a thick blue/grey coating that may be paint or some kind of deliberately oxidised layer.

The first and second variants seem to have steel parts that are largely plated with a silver coloured layer. The later two variants have steel parts that largely have a black oxide finish.

Being able to 'detension' your derailleur at the point of making a gear change was a French obsession in the 1940s and 1950s. Derailleurs were often supplied with double right-hand gear levers - one to operate the derailleur, the other to detension it. With hindsight, we now recognise all this as being an irrational cult, at least as irrelevant as the human appendix. It is possible that the second variant of the Huret Dural Competition is the earliest example, the patient zero, of this particular brain worm.

I think that this is an example of the third variant of the Huret Dural Competition, described above. I believe it is the 'fixed tension' version of my Huret Dural Competition (4th style). Some key features may be:

It has restrained, flat, pulley cage plates. The range adjustment screw threads into a boss mounted between the pulley cage plates.
There is a volute spring covering the exposed part of the sliding cylinder mechanism, to protect it from dirt.
The top end of the tension spring is mounted on a, rather elegant, adjustable, bracket, but this bracket cannot be moved while riding.
The hanger plate is aluminium.

This derailleur should probably have a small clamp on bracket on the adjustment screw to act as a high gear stop. You can see one of these on my Huret Dural Competition (4th style).