I'm fixing up an old bike I bought in Belgium. Not sure about the exact brand/year. The bottom bracket axle is branded "Flandria". It's a cottered axle. I want to replace this with a square taper bottom bracket. Details of my current bottom bracket:
- frame is 70mm wide (where to bottom bracket goes)
- threads are 24tpi, both sides screw in clockwise
- bottom bracket diameter is 33.9mm
I tried fitting a British style bottom bracket first (excuse my incompetence :) ). That didn't screw in because of the thread direction of course. The right threaded end does screw in easily, therefore my conclusion that it's 24tpi.
After that, I tried an Italian style one. The diameter of this is too large, so doesn't fit into the frame.
It can't be a French style bottom bracket either, as the frame is 70mm wide. My information source: https://www.sheldonbrown.com/cribsheet-bottombrackets.html