they only stay on the rear sprocket of a multi-speed set-up with the help of the rear mech.
This is mostly because of the shape of the teeth on the cassette sprockets, not the chain....compare a fixed sprocket to one on a modern "block".
@deleted started
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This is mostly because of the shape of the teeth on the cassette sprockets, not the chain....compare a fixed sprocket to one on a modern "block".