Originally Posted by Danhedonia

I put the cassette on. When I removed the 9-speed that's on there, I found what looked like a spacer between the hub and the largest cog. It looks to be about 1-2mm thick.

When I removed that silver-metallic ring, the new cassette fit perfectly; the locking ring had several turns before tightening. But I left that ring on, it was a close-but-that's-not-secure fit. Is that silver ring a crucial part, or am I good to go?

FWIW, without the ring, the distance from the largest cog to the hub didn't look overly close - but I suppose the best way to figure that out would be to drop it back into the frame (time prevented me) and see how it revolves?