I brought a french made frame which I guessed was from the late 50's.

Took my time to repaint it, and build it up with mafac duel forge brakes and other parts from that time. Its complete apart from I can't seem to find the correct rear derailleur that fits.

The rear deraileur hanger is a late 50's simplex - Imgur: The most awesome images on the Internet

I found a photo from the internet as it has better lighting. - Imgur: The most awesome images on the Internet

There is no tab for a simplex prestige, yet the threading is too thick for 1950's simplex tour de france like derailleur. - Imgur: The most awesome images on the Internet

Any ideas? Really should be french and late 50's. Trying to put the old simplex derailleur in was ruining the derailleurs threads.

1) Is there a period-correct Huret that would fit?
2) Can you mount a TdF with a different fixing bolt, one with the correct threads?

Others who know more about vintage French gear than I do may be able to suggest other options.

The Juy 543 would be a good choice over the Juy 59 as the Juy 59 is stupid expensive.

Agreed, but he is reportedly finding no "juy" in trying to mount a Simplex derailleur. Wrong fixing bolt?

The juy 543 is stupid expensive too!

oh boy. I have a feeling this bike is not going to get running for a long time!

One would think a late 50s Simplex dropout would fit a late 50s Simplex derailleur. Hence the Juy 543 and Juy 59 recommendations. Could also go with a Juy 60.

If the threading doesn't fit Simplex derailleurs, then it is a crap shoot.

Imgur: The most awesome images on the Internet - some derailleurs on the desk

Imgur: The most awesome images on the Internet - I was hoping this one,

Imgur: The most awesome images on the Internet - but the threading does not match, the frame looks closer to campagnolo threading.

I will have to go round my friends house and see what I can swap if they have anything that fits.

I was eyeballing a 1951 Italian frame a while back. Not expensive, about $200 shipped to my door. Had the 4mm adjustment screws and the cable stop at 4 oclock. This was specific to the first gen GS. Cool frame but I would have to buy a $2000-$3000 derailleur to make it work. I passed. Neat frame though.

Wish I had thought about this potential trap before I started. No I don't have a suicide front derailleur in my spares box either! $$

After looking at my other simplex 50's derailleur hangers which are not threaded like this - I am coming to the conclusion that the dropout has been modified to accept campagnolo threading and hangers. Cut and threaded.

Going to take my time but I think putting the simplex tour de france derailleur on here whether the hanger likes it or not. any objections? Its a repainted repaint frame anyway.

https://imgur.com/xMTl2sn
https://imgur.com/bE7XQKk

edit - normally I work on 70s and 80's bikes so I am learning as I go here

Actually, relooking at your first photo I agree, that hanger was modified to accept a Campagnolo GS. Stop at 7 oclock is a dead give away.

I am biased, but I'd run the GS. It is a $40 derailleur and it shifts better than any coil spring RD imo.

can you get the threads checked, and the make the necessary adaption?

and the Simplex installation instructions
https://veterancycleclublibrary.org.u...20Library).pdf

You need to post pictures of your actual dropout that "you guess" is 1950's. The pictures you posted don't fit that description. Your "duel forge" brakes don't exist.

I interpreted as meaning MAFAC Dural Forge
well taken photos in natural filtered light with a neutral background are always appreciated.