Originally Posted by
Kayce
The main difference between a dirt cheap cog, and anything else is the dirt cheap cogs are stamped out of sheet metal rather than forged. A forged cog is stronger, has a better tooth profile and rounder.
This. ^^^
The threads on the cheap stamped cogs can also be sketchy and can damage the hub threads in the case of a poor fit. I've never bothered with the fancy-pants EAI Deluxe or Phil cogs; those black oxide treated Dura-Ace cogs work fine and give a better bang for your buck.