Huret Allvit (1800? 1960 version) derailleur

The Huret Allvit was a milestone in derailleur history. It was the first parallelogram derailleur designed for the mass market. With its wacky parallelogram geometry and its pulley cage pivot concentric with the guide pulley, it made a real attempt to maintain an even chain gap and provide a decent change over 14 to 28 tooth freewheel.

In its various guises the Huret Allvit was the first French parallelogram derailleur and the first derailleur from any nation to break into the all important American market for leisure bicycles.

Despite this historic role, I always disliked it. It weighed a ton, its adjustment screws were all over the place and most of all it had too many small plates joined by too many dodgy pivot bolts. In British weather, maintained by oil-shy British cyclists, it either rapidly loosened off and became horribly imprecise or it rusted solid.

The Huret Allvit was one of the longest lasting derailleur designs in history. There is an untold number of different variants - certainly more than 30. These can, perhaps, be best understood by dividing them into 4 'eras', which are defined by the design of the main arm:

The first 'era' ran from 1958 to 1960. During this period the main arm was largely flat and the parallelogram mechanism was in full view. I have been told that these models had model numbers in the 1800s - although I have never seen this in print.
For the second 'era', from 1961 to 1967, the main plate was completely redesigned to become the Allvit's signature wrap-around body, encasing the paralelogram mechanism. The main plate had a flattish area around the head of the b-pivot bolt, but had a pointed reinforcing rib running down the rest of its length. These models had numbers in the 1900s.
1968 to 1975 saw a third 'era'. The main arm was again redesigned, losing the reinforcing rib and gaining a triangular, almost heart-shaped logo. The model numbers were still in the 1900s.
The fourth 'era' ran from 1976 to 1983. I personally never saw many problems with the main arm, but in 1976 it was redesigned again, now with what could almost be described as buttresses around the head of the b-pivot bolt, and the return of the pointed reinforcing rib running down the rest of its length. Now the model numbers were initially in the 2500s and later in the 2700s. The last Allvits were probably produced in 1983.

So I hope that's clear then!

Focussing down onto the first 'era' some of the variants include:

Launched in 1958, the very first model was often shown in adverts and Daniel Rebour drawings - but I have never actually seen one. It had a thick, 3.9mm, steel main plate which did not 'encase' the mechanism, steel pulley wheels with 8 holes drilled in them and a parallelogram spring that engaged with a hole in the main plate.
In 1959 the pulley wheels became solid, with no holes, and the parallelogram spring was changed to hook around the edge of the main plate. This version definitely existed and was manufactured in some volume.
For 1960, the main plate was changed from 3.9mm thick steel to a mere 2.8mm thick steel . To add back strength the main plate gained a couple of reinforcing ribs, one of which was long and pointed and became a recurring theme in Allvit styling.

This is a rusted and well used, 1960, Huret Allvit. Some of its attributes are:

The main plate is 2.8mm thick, does not 'encase' the mechanism and has reinforcing ribs.
It is branded 'Huret Allvit' on the side of the main plate.
The parallelogram spring hooks around the side of the main plate.
It has circular steel pulley wheels with no lightening holes.

Note that, despite the reduction in thickness of the main steel plate, this derailleur weighs the same as the 1959 version. How did they manage that?