Just throwing in my two sense... I have used Soma cogs on all three of my fixies for over a year with no problem. They threaded fine, seem to wearing fine and have shown no signs of bad machining. FYI, I run no brakes and skid/skip, so they are under a lot of stress. Are they that much cheaper than the alternatives? Prices seem pretty compariable... http://sheldonbrown.com/harris/fixed-sprockets.html