I have a 1968 Raleigh Super Course in close to excellent condition that I have converted. I bought new Velocity wheels and changed it into a Fixer. I kept the original cotter crankset and now I'm having problems. I have been warned about keeping my beautiful crankset when going fixed, but being suborn,I kept them on anyway. This crankset is the original cotter Stronglight that came with the bike... I love 'em. Now they are slipping. Ugh.

I need to change them out now, and here comes my question...

does anyone know about these threads for the lower bracket? Are these bikes hard to convert the crankset? Any suggestions on which lower bracket to use?

Any imput will help...

Thank you!