It's a cassette hub, where all of the gears/spacers are stacked on, then tightened down with a lockring on the end near the dropout. THIS freehub uses the last cog as the lockring, so if I make a a single speed, there will be the driving cog, then one out on the end doing nothing but looking strange. If I can find a lockring of some sort, it will take the place of the cog on the end.,,,,BD