I need to replace a cassette, and the last time I did it, which was the first time, I noticed the cogs all come apart. So my question is, why can't I just flip the cogs around, so the wear is on the other side of the teeth? I have already ordered a new cassette, but I thought maybe this is a way to get a little more life out of one? And I did notice grooves in the cogs, on the outside side, that they all have. Do these serve a purpose? I'm talking about the ones to the left of the teeth number in the photo.

I think I have a SRAM cassette, but I don't know for sure. Came with the bike, I'm at work, at the bike I'm talking about is at home.