Davidc
Guru
- Location
- Somerset UK
This is the Sheldon Brown page with the measurement and wear information. The Park Tools thing with the prongs is easier and less messy though.
I tend to go through 3-4 chains per cassette so no, new chain doesn't equal new cassette.
However, you can't use a new chain on a worn cassette.
If this is the case [too much stretch] then you will need a new cassette to match the new chain. I can't see how it's dangerous, it's just either annoying, or makes the bike unrideable.