The 5401 is a direct replacement for both the Glacier Bay and American Standard models that are equipped with a 540 Flapper and flush system. The 5403 is a universal replacement for most 3 inch flapper and flush systems including Glacier Bay and American Standard. The 5403 comes with on additional adjustment for the hinge, it allows the flapper to attach to wider 3 inch systems that are not Glacier Bay and American Standard.