Originally Posted by
jameswelle
What would cause this? Would the male threads on the cup and the female threads on the shell fuse together if the bottom bracket was never serviced and removed?
It's most likely a result of electrolytic corrosion. This is always a risk when dissimilar metals come into contact. Using an anti-seize compound on the threads would likely have prevented this.
As the shell was originally tapped as English, it is likely possible for it to be retapped to Italian dimensions. Otherwise, a threadless cartridge as suggested above would also work.