johnopower

I'm pinching a Svelto rear derailleur off an old track ended frame... the rear derailleur bolt attaches to an adapter/brace, also mae by huret, for use wth nutted axles on track end frames. I took the adapter off and bean screwing the derailleur onto another steel frame, this one with campy road dropouts from the 80s... three turns in (by hand, i was cautious about french threads) and it became very, very tight... that kind of tighness taht doesnt stop, but kind of strangles until you think youre really makinga mess of things. so i stopped and took it out. oh, and this wasnt a "track" frame, but had the same kind of ends... is there a name for ends like those on a track bike, that are found on old roadies?
My question is, (and i know i could answer it if i had a thread guage, but i dont), are old huret rear derailleur bolts threaded differently to modern, japanese or italian versions? and, if anyone knows, were these derailleur+adapter jobs made to only work together? or are there french rear derailleur threaded frames out there!?
this is a photo of a similar setup...
https://images.andale.com/f2/115/106/..._long_cage.jpg
thanks for anyones help!

T-Mar

Everybody (Shimano, SunTour, Huret, Zeus) uses derailleurs and dropouts with a gear hanger thread standard of 10mm X1.0mm. with the exception of Campagnolo, who opted for a 10mm x 26 TPI standard. The difference between 1.0mm (25.4 TPI) and 26 TPI is just enough to make things tight. However they are close enough that it will work, but with some damage to threads. The prefered method is run a 10mm x 1.0mm tap though the hanger to minimize the damage. Once you've made the awitch, is not advisable to be switching back and forth between Cmapgnolo and other derailleurs.

johnopower

perfect! thanks so much.... very very impressive bit of info
After reading your response I searched for more info (specifically if all campy dropouts sport hangers with 26TPI threads, and yes, they do! I dont nkow how many frames I've switched stuff over with, going from campy to otherwise... amazing that I didnt know about the difference until now.
Apparently is a class B fit (which means acceptable) according to the BB institute.

Thanks again!

T-Mar

It's difficult to understand why the Italians settled on bicycle thread standards that combine a metric nominal diameter with an imperial thread count. That is just insane engineering and means the industry has proprietary taps and dies. Fortunately many of the threads used on Italian bicycles are close enough to an English/BSC threading that they are a class B fit. Most people think that French threading is the anomaly, but at least it is all metric and the taps and dies (at least in the samller sizes) can be bought off the shelf in hardware and automotive stores.