First, let me start by saying that I have read Sheldon's article on this topic. I'm asking to verify that I understood it correctly.

I have a bunch of Regina freewheels that I got second hand. Some of them are hand-marked "FF" but I don't see any other visual clue as to what the threading might be. I have, as a result of the same purchase, some hubs that are very clearly marked as to how they are threaded. As it turns out, I have at least one each of British, Italian, ISO, and French. I would have guessed that maybe the "FF" marking indicated French threading, but that seems not to be the case. That's where my question comes in as to whether or not my understanding is correct.

Here's an example of what I'm looking at.



So what I thought was this:

1) Any freewheel will thread on (at least loosely) to a French threaded hub (though only French threaded will actually be safe to use that way).
2) A French threaded freewheel will bind if I try to put it on any non-French threaded hub.
3) The only possible way to distinguish between British, ISO, and Italian threading on an unmarked freewheel is by judging how tightly they fit.

Have I got that right?

I don't remember the exact results of my experiment except that at least one of the freewheels started to bind on an ISO-threaded hub and at least on of the freewheels that was marked "FF" did not.

These are corn-cob freewheels which I'll never use. They are in excellent condition so I'd like to find a new home for them, but I'd like to be able to tell prospective new owners what they actually are with some confidence.

FF is typically French threaded. It is usually stamped, not scratched on.

If a remember correctly a BB cup can be used to check Italian/English.

It appears to have two grooves in the back, that is French.

Generally, a vintage freewheel with no markings has threading that is native to the brand's country. Regina freewheels with no markings are Italian threaded. The majority of Regina freewheels would be used by the Italian industry, so not adding identifiers to freewheels with Italian threading makes the most economic sense.

The freewheel threading standard would be marked on the back on the body, not the cogs, as the cogs are interchangeable. Regina used F.F. or 2 grooves to signify French threading depending on the era. It's hard to tell in the photo, if the body has 2 grooves (French) or 3 grooves (ISO). What appears to be a 3rd groove may just be the thread start.

OK, that's potentially very helpful. Looking back at my pictures, one of the freewheels that was hand-marked as "FF" is a Japanese (SunTour?) 7-speed freewheel, which seems fairly unlikely to be French threaded, so maybe that was the one I'm remembering as having threaded smoothly onto an ISO hub in spite of the "FF" mark.

I'll look closely at the grooves when I get home. For now, I have these additional pictures of one of them. It looks like one groove, so Italian threading?



And then this was the 7-speed freewheel:

That's an interesting idea. It would be particularly helpful in this case since the stupid Park Tool FR-4 won't fit over the Campy locknut.

FF = file Francese ("FEE-lay fran-CHAY-say") = Italian for "threads French" = well, you get the picture.

So whoever scratched "FF" in the 7-speed freewheel was probably just wrong?

SunTour used to stamp a small M on the body where a freewheel tool would engage to indicate Metric/French. I have at least one of their Perfect freewheels like this. I assume they would also do the same on the later Winner freewheels like you have posted, but do not know this to be the case. I have also seen Perfects with Metric spelled out and with 34.7 x 1.00 notation in that same location.

No, it has two grooves. It’s likely French. They probably scratched it In for an obvious visual clue.

Yes, a known English thread adjustable cup will thread into an English thread freewheel body.

As noted above, some freewheels have arcane markings to indicate thread spec:


Source: Sutherland's 4th Edition

Here's some thread details that I compiled to go along with what others have posted.

FRENCH 34.7 mm X 1mm (1.366” x 25.4 TPI)

British 1.370” x 24 TPI (34.8 x 1.06 mm)

ISO 1.375" x 24 TPI (34.9 x 1.06 mm)

ITALIAN 35 mm X 24 TPI (1.378" x 1.06 mm)

French threads have the smallest outside diameter. ISO, British and Italian freewheels will start to thread on but will bind up after a few turns. If those freewheels are forced on they will damage the metric threads and can spin off under load destroying the hub.

ISO and British freewheels are interchangeable.

ISO freewheels fit Italian threaded hubs.

Italian threads have the largest outside diameter. Italian freewheels can be used on British threaded hubs but should not be switched back and forth with British freewheels.

Are you sure you don't have that backward? I'm experiencing the opposite, I think. French threaded freewheels will start to thread onto non-French threaded hubs, but will bind after a few turns.

So the responses in this thread have been very helpful. Now that I'm home and can lay hands on the freewheels, here's what I'm seeing.

A) Two Regina freewheels with gold-colored cogs, both hand-marked "FF", both have two groove, a BSA bottom bracket cup starts to bind after about a turn and a half on either one.

B) One Regina freewheel with silver cogs, not marked "FF" in any way, has a single groove, a BSA bottom bracket cup threads onto it smoothly until it bottoms out.

C) The SunTour Winner 7-speed freewheel from post 6 above, hand-marked "FF" on both a cog and the back of the freewheel mechanism, a BSA bottom bracket cup threads onto it smoothly.

So, as I indicated above, I think the hand-markings on the SunTour freewheel are just wrong. I had previously not noticed any marking on the top of the mechanism, but with a little digital assistance here it is:



Does the "GE" there (at the 10 o'clock position) mean anything? What about the squiggle below that?

It seems this is my squiggle:



JIS -- is that the same as ISO?

No, British freewheel threads are .004" - .002" per side larger, ISO threads are .009" larger - .0045" per side and Italian freewheels are .012" larger, .006" per side so they will fit over the outside diameter of a French threaded hub.

The problem is the difference in the thread pitches. At 5 turns there's a .0115" or 0.295mm pitch error. See graphic below.

Aluminum threads on hubs are soft. Forcing a British, ISO or Italian freewheel on a French hub will deform the threads, weakening them. You are essentially re-threading the hub producing very weak threads.

A 1mm pitch thread has a theoretical height of ~ .046mm (.025" for 24TPI). You will mush off the top 1/3 to 1/2 of the threads by forcing a 24 TPI freewheel onto to a 1mm thread pitch hub. There's not much material left.

If you put enough force into the weakened threads like honking up a hill, you can easily spin the FW destroying the remaining threads and trashing the hub, especially with Italian on French.

Been there, done that. Means not being able to pedal home. Someone else did the misfit not me.

No, JIS stands for the JAPANESE INDUSTRIAL STANDARDS (Committee).

ISO is the INTERNATIONAL ORGANIZATION FOR STANDARDIZATION.

While both of them use mostly metric dimensions there are differences in thread forms and other details.

OK, that's maybe starting to make sense for me. The French threaded hub I was testing with wasn't laced to a rim, so I didn't go many turns before backing things off. Nothing I tried seemed to have a problem, but maybe it would have if I had kept going.

But the reverse is also true, then, right? A French threaded freewheel will barely start on ISO/British/Italian threaded hubs because they have larger threads?


Yeah, I realized they were different things. What I meant was, is it the same threading in this case? I can't find any specification for JIS freewheel threading.

I was sold a Suntour with the "M" on it and it was not French, so not a 100% thing. I have also seen the "M" on a Suntour on the backside of the body. That one was French, but I have no others for further support. Best bet is to find a thread gauge to check. Thread gauges are cheap at your local hardware store.

FWIW, I have a SunTour freewheel that is explicitly marked as metric thread:

Date code.

G=1990 E=May

Also been there. In 1964, I installed a BSA sprocket on my new Helyett Speciale track bike, which was built with all French parts. Wasn't long before the sprocket broke loose under load.

The mechanic at the bike shop took off the sprocket and wrapped the the threaded portion of the hub in aluminum foil. That quick-and-dirty repair held up for the next couple of years, until I sold the bike to a fellow who used to post on here using the name Stronglight. That was the beginning of his fascination with French bikes.

Here's an odd freewheel that I ran across. It looks like a Regina and stamped S.I.C.C. and MADE IN ITALY but it's marked ATOM???

Since I have a lot of French bikes, I've squirreled away a box of French threaded freewheels - Atom, Regina, Suntour and Shimano. I'll have to look to see how they're marked.