Japanese Sugino 'French' threaded bottom bracket on a Peugeot frame. 35mm x 1mm
I'm not really the tech type but this is as about as tech as it gets when restoring that dusty old French bike.Hopefully,this will help you avoid the pot holes that I fell into when rebuilding my first vintage treadly. (I have absolutely no idea why it is called a bracket,when really it's a bunch of ball bearings and a spindle)
French bikes prior 1980, had a unique 'French' threading. Virtually all other bikes had 'British' iso threading.French bottom brackets had a diameter of 35mm with 1 mm per thread(this equated to 25.4 threads per inch aka 25.4tpi) whilst British threads were 1.37" x 24 tpi. From this you can see that French bottom brackets had finer threads and more of them. I wish I knew this when I rebuilt my first Peugeot UO-10. Wanting to replace the nasty cottered cranks with some shiny new ones I toddled off to my LBS. Not to worry ,the helpful man said, as he sold me a set of Shimano iso Alfine cranks and bottom bracket. He then,kindly,sold me a super long wrench to torque it right in. This set up works perfectly well, however I now know that the threads in the bottom bracket shell are pretty much stuffed, and will be of no use when the time comes to replace the BB.Not to worry, as there are a number of good options on the market. For more detailed info, check out the page on the right hand side.