I rebuilt one of these last summer. Originally I planned on making it my first fixy, but decided that since the frame was too large for me this wouldn't be wise. Still use it as a 10 speed. The bottom bracket is definitely the Raleigh threading as the poster earlier said. The spindle is also a slightly different size than what is used today, so you would have to replace the whole bb or none. I would suggest just going to your lbs and having them put in a new bb cartridge, because cottered cranks are a pain. I had to get new pins, but the pins were different than what is available now, so I also had to grind the new ones down to the right shape.