Cassette 8g PG-850/830
Cassettes from Sram are available in several qualities and the more expensive you choose a cassette the longer it lasts, make sure you choose a chain of a similar quality otherwise this theory does not hold.
The cassette is placed over your rear hub and secured with a locking ring at the end which is tightened with a key (puller) that has 12 pins.
The locking ring comes with this item
Guide to changing the cassette