Stop a running toilet with the Fluidmaster 500 Universal Toilet Flapper. Unlike flexible flappers, the 500 flapper features a solid frame that doesn't twist for the best seal every time so you never have worry about jiggling the toilet handle again! The 500 Universal Flapper is best suited for use with 3.5+ gallons per flush toilets. Only Fluidmaster has toilet flappers with built-in Microban® protection. Not just simply a coating, Microban® is specially built into the construction of our flappers to fight flapper breakdown and combat bacteria.