Jerry Moos was eloquent, but I'd still add a note or two:
JM: Well, I wouldn't go quite that far, but I'd say with Lyotard, pedal thread was highly negotiable. A couple of years ago, I measured a large number of Lyotard pedal axles, including several Berthets and found they celebrated the French belief that consistency is the demon of little minds.
JM: One must remember that French pedal thread is nominally 14.0 mm, while English 9/16" is nominally 14.2875 mm, which isn't a huge difference to begin with. With Lyotards, the diameter was pretty much randomly distributed between just under 14.0 and about 14.3 mm. I do think the ones marked as French (D &G or no marking) averaged a little closer to 14.0, while the ones marked as English (R & L) averaged a little closer to 14.3. But a lot, including some with each marking, were about half way in between. I don't think Berthets are any worse in this respect than most Lyotard models.
Harvey: I believe that the only Berthets I have left are very late production, with (would you believe) both 17 mm male hex and a 6 mm Allen key. With two different vernier calipers (one with dial), they are 13.8, but only a slight taper to the threading, within my uncertainty. And, they are marked "R" and "L"... Another set of Lyotards, these with R and L embossed on the spindle ends, are significantly under 14 mm, too. It must be my tools, of course.
JM: A couple of years ago, TA deliberately sold some of the otherwise classic TA pedals deliberately designed and touted to fit either French or ISO cranks. I have a couple of pairs, and it actually seems to work. I haven't measured a large number of th TA's, but knowing TA, I expect they very consistently split the difference between 14.0 and 14,2875, while Lyotard used the scattergun model of statistical control. One other thing, I think Berthets came with three different wrench flat sizes over the years. 15 mm of course, but also two others, can't remember which two among 14,16 and 17.
viva la difference!
mcLean va usa