So I was doing skids in a wet parking lot today, and my cog was slipping on my hub. This is the second time this has happened. I get home and tighten the cog and lockring--hard. Rotafix for the cog, lockring tool for the ring. Before I did this, I removed them to have a look at the threads and make sure the cog was adequately greased. The hub threads looked normal, but there was a small ribbon of aluminum--maybe .5 mm wide and very thin--stuck to one of the threads of the cog. Is this something worth worrying about, or should I just not sweat it as long as the cog stops slipping? It's a Formula hub, EAI cog, DA lockring. Oh, and before I get crap for noob questions, yes, I did use the search feature.
Assuming you're using an aluminum EAI cog and you're sure your hub is okay, it sounds like you've stripped your cog partially. Get a new one. Someone else can chime in on this, but are the EAI cogs wide enough for the Dura-Ace lockring to fully tighten against them? Either you didn't torque everything down enough in the first place or something in your setup isn't quite compatible.