This is a replacement filter for Hoover FoldAway, and TurboPower 3100 models. Will fit the following Hoover Models; U5170-900, U5172-900, U5175-900, U5179-900. Designed to fit Hoover part #’s 43615-090 (40130050). This filter should be replaced at least once a year. For homes with severe breathing issues such as asthma, or homes with severe allergies should replace this filter every 6 months. This is the main filter for the vacuum cleaner. The more often your replace this filter, the longer your Hoover bagless upright will last you.