This red part is what seperates the dirt from the air and keeps it in the collection area of the cup. Is required for use. To clean this red filter twist and pull out. Is needed for the vacuum to operate correctly. Used in battery powered Hoover LYNX BH50010 & Signature BH50020. Also for corded model Hoover SH20030. Substitute part # is H-517758003 When sold out price will show $00.00. 3/21/22 dda