From Sheldon Brown:
"3" series spindles normally fit 68 mm ISO/British/French bottom brackets.
"5" series spindles normally fit 70 mm Italian bottom brackets, also 68 mm French with thin cups.
"7" series spindles fit "oversized" 73 mm ISO/British bottom brackets, sometimes also work with Raleigh 26 tpi cups in older Nottingham-built Raleigh bikes .