bros---- dudes---- the cassette slides onto a body---- the body contains the little spring and teeth--- over time and even hard use can mess with this component--- I run a american classic a10 speed body-- aluminum-- its pretty sturdy- but the slots are indented from racing crit---- If the cogs are not tightly bound- the flex will take its toll on the body---- most bodys are replaceable--- not quickly--- but serviceable--- I see many low end cassette bodys fail---