Originally Posted by Explosive

So, if you read my tire mounting debacle we've progressed lol. Im sitting here with my new 105 cassette in hand about to install on my new wheel. This is the first time I've done this. On my hub was a small metal ring, one face was flat and the other side has three small recessed areas.

I tried googling and appears this is a spacer for 10 or 9 speed cassettes ? Is this correct ? Every cassette install video I've watched doesn't seem to use this ring.