Originally Posted by
Again
Nothing fit on anything, either sides. Anyway, when I order a 9-speed cassette, am I to expect a cassette with 9 sprockets or a bag of loose parts?
I respectfully posit that you either have a wrong-speed cassette ( like you ordered a 9-Speed, but you have a 7-Speed), or you have no idea how to put a cassette on. There is nothing wrong with the cassette in your picture.
I think you need a bike shop.