Originally Posted by LóFarkas
Put questions like this in the SS/FG subforum... You would have been told 5 times within 3 minutes of your post: "BB lockring".
Old bottom bracket lockrings used in loose ball BBs have the same size and threading as the hubs, so they spin on nicely. About 1,5-2mm thick, I guess, should be under $1 or free in your lbs. Make sure that the lockring still has enough threads so it doesn't strip.
Not exactly, the BB lock rings are inconsistant, and cheapies only have 1 finished face. Furthermore, a used one will likely have burrs on the notches from the lockring wrench. A lock ring is a lock ring, a spacer is a spacer. There are spacers made to go between hubs and freewheels which are the exact size for your track cogs . they come in consistant sizes 1mm, 1.5, 2. & your LBS should have some. I would NEVER use a BB lockring as a spacer on any of my fixed gear hubs.