I never knew I would need to change this filter but I'm glad I did. It snaps securely into my Dyson DC17 and acts as the final filter on the base/rotating brush through which the exhaust exits. The previous one, which was about 5 years old, was literally pitch black. I'm only giving 4 stars because this filter still has a chemical plastic smell after about 5-10 uses. I don't know if the OEM would have done the same (probably would) but that's about all I can beat them for.