Originally Posted by eyefloater
IRO / Formula - I believe the "IRO" version uses longer axles (still spaced to 120mm though). The black ones you can get fixed/fixed, but the silver ones are only available fixed/free. These days, 32 vs. 36 is a non-issue unless you're heavy, touring or paranoid.
I've got a silver fixed/fixed IRO hub on my bike. No problems so far.