[Lab Worker]

For a Campagnolo cassette you will need a Park BBT-5. This tool will work on the cassette locking ring and on the Campagnolo bottom bracket cups (if you use a Campy BB)

Does the HUB say "12/13 tooth" or the LOCKRING? The included lockring should be for 12/13 tooth cassettes, if you want to use an 11tooth Campagnolo cassette then the cassette will include the lockring.

 

[Lab Worker]

Lockrings are smaller for 11 tooth cassettes than for 12 and 13 tooth cassettes, as mentioed by Terry B. They are not interchangable.

Campy do a strange thing with lockrings.

If you buy a cassette starting with a 12 or 13 tooth cog, the cassette will not include a locking.

If you buy a cassette starting with an 11 tooth cog, it will include a lockring.

If you buy a Campagnolo hub it will include a 12 tooth lockring.

Most afermarket hubs do not include a Campag lockring, which means you usually have to pay extra for one. DT Swiss are nice enough to include a lovely CNC aluminum lockring with their Campag rear hubs.