Allergen filtration cartridge filter fits in dirt cup of all Hoover Foldaway models in the 51000 series and Turbo Power 3100 including these popular models: U5162906, U5162911, U5164900, U5165900, U5167900, U5167950, U5170900, U5172900, U5173900, U5173950, U5174900, U5175900, U5175950, U5176950, U5177900, U5178900, U5179900, U5179906, UH40155, UH40185, UH40190.