This is a Huret Eco from the 37th week of 1981. It will work on six-speed (12 speed) easily and is actually designed for it.
This is some info from Dirsaeligears:
To replace the venerable Svelto, Huret took their Challenger/Success design, tweaked it by increasing the cage length and rendered it in their very best pressed steel and rivets. Note how, as standard, the pulley cage is attached in the lower hole (labelled ‘28 teeth’) in the front knuckle. The upper hole is labelled ‘24 teeth’.
Huret’s timing was good, because the Huret Eco (short for economical not for ecological) was able to benefit from the rise in prices of Japanese derailleurs as the Yen revalued. Europe and Japan had swapped places - with Europe supplying the low-price, low-tech, steel Eco and Japan supplying the higher-price, higher-tech aluminium SunTour Vx and Shimano 600.
The Eco gave survivable performance at a very low price. I have to confess that I personally (slightly reluctantly) sold, fitted and repaired hundreds of Eco’s.
Hope that helps!
