Specifically French vs. everybody else. I have a reason for asking.

Whenever I've replaced a French freewheel it was with one from another French bike of similar vintage. Consequently I've never had to worry about the threading. Now I have reason to worry that someone else (not me, honest!) may have forced a non-French-threaded Suntour freewheel on a French hub. It's a long story, not worth going into juts now...

What I'm curious about is whether they might seem to fit when they really don't. Loose, tight, start-easy-but-get-tighter? That sort of thing. PM me if you wish for further details of why I'm asking.

Thanks.

the diameter of FR versus BSC is that the metric FR will be ever-so-slightly smaller than the BSC (34.7mm compared to 1.37" or 34.8mm). However, the real differences are the threads themselves: metric threads are 1 per mm (close to 25.4tpi), the BSC is 24tpi so that's where the jamming and damage will occur. Since the hubs are softer alloy and the FWs are harder steel, some monkey could ram a FR FW onto a BSC hub, once, and it might stay there, but if you remove it you'll probably get a bunch of metal shavings and see a ruined hub shell. The other way 'round (BSC FW onto a FR hub) in my experience is usually too loose feeling to inspire anybody to keep trying to force it...it not only doesn't give a good thread-feel, but also seems sloppy and so likely to cross-thread. Again: an idiot might persist.

Everything you could ever want to know about freewheels, from the late Sheldon Brown.

https://www.sheldonbrown.com/freewheels.html

If I can add anything, it would be from
the perspective of a guy who weekly
gets a fly's eye view from the wall looking
onto the various degrees of mechanical
ineptitude that wander through a do it
yourself bike coop.

Can a standard threaded freewheel be
forced onto a french threaded hub by
the clueless? Absolutely, happens with
alarming frequency. Is the hub ruined
in this case? Pretty much, although if
you just leave the wrongly threaded
freewheel in place, the wheel can give
quite a bit of service still in most cases.
I guess it has to do with all those loose
metal shavings that used to be threads
now acting as filler.

I'm afraid that in the rough and tumble
world of do it yourself bike maintenance,
the sad fact is that bozos rule. When
somebody doesn't know enough to even
know what they ought to be asking about/
careful of, you're just gonna have a fair
amount of collateral damage. I try to
view it as "learning experience", but I'm
not always sure how much "learning" results.

There's one poor orderly soul who does yeoman
service as a mechanic manager at our shop who
I fear will someday have a stroke if he witnesses
yet another particularly egregious abuse of tool
(and I am not using this as a euphemism for
self abuse in this instance).

Mike Larmer

p.s. as an interesting side note, did you know
that m*sturb*tion is one of the forbidden
words that the forum server is programmed
to block?

you spelled it wrong.

Well, ah, that's certainly informative to some degree. Not sure what degree though.

Thank you unworthy1 for a nice answer. Reading thread specs is one thing but feeling the effect in your own hands is another. I gather that a mismatch would at least be noticeable and probably enough to indicate an error to a non-idiot. A phone call a moment ago also gave me reason to believe that whoever worked on this hub was most probably not an idiot.

The world is a fascinating and mysterious place, especially when a bike of unknown history is involved.

Thank you all.

Sometimes BSA freewheels can be threaded onto French hubs. Sometimes they skip on the skip on the threads, sometimes they dont. sometimes they thread on all the way, sometimes they dont. If you have a French hub thats slightly oversized and a BSA freewheel thats slightly undersized it'll be less likely to skip the threads. Conversly, if you have a lsightly undersized hub and a slightly oversized freewheel it'll be more likely to skip threads..

On a related topic, I've heard that and Italian and English threaded compnents can be interchanged........with a little careful "persuasion" I'm skeptical, but more like scared to even try, but is this true?? If they are so close, why did they even bother to have two different standards??
at least the French stuff is different enough to maybe justify their existence....maybe....

Chombi

The difference between Italian and English is in the profiles of the threads, making it a "class B" fit. The conventional wisdom is you can put a BSC freewheel on an Italian hub, but should not change back and forth thereafter. The same goes for an Italian freewheel on a BSC hub. When I have tried to put an Italian freewheel on a BSC hub, I have felt an uncomfortable amount of resistance.