Rear cassette

[zotty]

Is the depth of the free wheel hub the same and the later cassettes put together with slimmer gears to allow more of them?

got me there lol.. i know the gap between sprockets got smaller.. 9 and 10 speed cassettes use narrower chains... (can of worms).. theres chains for 5 speed and chains for 6 speed.. then theres chains for 7 and 8 speed... theres also chains for 6/7 and 8 speed.... mine field? lol