I believe I have some English hubs that may have had French thread freewheels forced onto, since they are Japanese but will now take either freewheel w/o force. The French freewheels I'm threading on are 1950's-60's Cyclo and Moyne, so definitely French threaded.
Measuring thread OD gives very small differences between a big batch of hubs, some known to be French-thread. I've seen a few French hubs that only bind up when an English freewheel is ~80-90% of the way on.
I've got a couple of Peugeot wheelsets that have been using Shimano freewheels for some time. Does anyone know when Peugeot changed their threading to English? My 1979 UO9 SuperSport has, curiously, a Brit-threaded bb, and I installed an English Suntour freewheel on that bike a couple of thousand hard miles ago. As well, my 1979 PKN10-E came with a big Shimano freewheel on it courtesy of the prev owner, and it too has now thousands of miles with a smaller Shimano freewheel on the red-banded Atom hub.
So, the identification of French threads can be confusing, although I can sometimes detect thread distortion visually after a French thread freewheel has been forced on. Since the pitch is different, the individual threads will look asymmetrical, pushed this way and that.
Is there a link for ID'ing Campy French, English and Italian hubs? Is the banding consistent over the years 50's thru `80's? Many of my hubs have me scratching my head, and I'm starting to wonder if it matters, i.e. would normal road-double gearing result in failure?
David Snyder Auburn, CA usa
French threaded freewheels and hubs are a common trap for the unwary vintagista. The french freewheels are a hair smaller than the english. The problem is an english threaded hub will accept a french freewheel and feel okay going on, but the freewheel will be loose: loose enough to damage the threads and ruin the hub, especially under high torque pedaling like a tandem going up hill. And the French very seldom mark the thread size, which is 34.7 mm x 1mm for french and 1.370/1.375 x 24 TPI for english. Beware, in addition to french brands (Maillard, Normandy, Maxicar, Pellesier, etc. etc.) there are a lot of Zeus french threaded hubs on the market right now.
The only safe detection method is to have a known french freewheel to try on hubs. I now keep an old cyclo body lying on the bench to interrogate new hubs that arrive. A french freewheel will start to thread onto an english hub and then bind quickly within the 1st turn or so. As Sheldon Brown said, a french freewheel cannot be screwed onto an english hub without considerable violence.
Without a known gallic threaded freewheel, pull the Maillard freewheel off the Maxicar hub and try it on a known english hub. If the Maillard binds quickly, it's french, the hub is french threaded and the Suntour perfect freewheel cannot be used safely, unless you want to try the teflon tape trick mentioned by Jan. Like him, the thought of that trick makes me shudder, especially on a tandem. Note: Suntour did make some french threaded freewheels, but they are marked with the thread size, I believe. In any event, they are rare bird indeed.
If the maillard freewheel threads onto the english hub, you still aren't home free, as you then have to determine if an improper freewheel was installed on the Maxicar hub. I'd recommend getting a french freewheel to test for sure. Fortunately, with the proliferation of French sellers on ebay now, french freewheels are becoming more common although not in touring sizes. But a trashed 5 speed 14-19 is all you need for testing. Try to get a splined malliard, so you will have less trouble getting a freewheel tool for taking it back off again. Ah, what I wouldn't give for a french threaded 14x31 regina oro---.
Go to it, Sherlock
Tom Adams, with 3-4 sets of accidental french hubs lying around the house in Manhattan, KS USA.