The bottom bracket is really the bearing assembly that your cranks turn round and round on.  The bracket is made up of two cups, a spindle, a lock nut, ball bearings and, from time to time, a protection sleeve and ball bearing cages.  This entire assembly fits into the bottom lug where the seat tube and down tube join together.

Basically, there are three bottom bracket to consider.  First, there is the English BB.  Second, the Italian BB and, of course, the French bottom bracket.  None of the above are interchangeable.  And the French one is the least interchangeable of all.

The Italian bottom bracket housing (some Mexican also) is 70mm wide.  All others, be they from England, or Asia or anywhere just about, are 68mm in width.  Benotto bicycles, those made in Mexico, also sport the 70mm wide bottom bracket housing.

The French bottom bracket is intended to fit into the 68mm bottom bracket housing.  However, the threads are, as one might expect, considerably different than either the Italian or English offerings.  The threading difference and diameter of the cups is what makes replacing French bottom brackets more difficult.  That said.

The French threaded cups sport a 1.378 x 25.4 threads per inch(tpi) while a British(ISO) bottom bracket offers 1.3702 x 24 tpi.  Needless to say, the French BB will not even fit into a British housing.  Additionally, the fixed cup features right hand threading, while most others sport left hand treads.  Getting these Old School French bottom brackets was, at one time, a bit of a problem.  But no longer...

Fortunately, in the rapidly increasing interest in the vintage bicycle, and restoration opportunities, after market manufacturers are beginning to produce reproduction items.  A few years ago, finding a decent condition, yet alone New Old Stock (NOS), French bottom bracket would prove to be a challenge.  Today, it is a simple as Googling - French Bottom Bracket.  However...

To make things even more difficult, some French bottom brackets are different from other French bottom brackets.  Motobécane, for example, uses a different bottom bracket, the difference being thread direction.  Standard French bottom brackets use a right hand thread on the fixed cup side, but not the Motobécane.

Needless to say, this can and does create confusion but once that elusive or not so elusive bottom bracket is found, the next thing to consider is the crank set.  Is there anything special that the restorer needs to know about French crank sets and how they differ from most others.

NEXT - FRENCH CRANK SETS