1/2 thick flange comes with gasket. This extension is used for replacing, repairing, retiling bathroom floor. Installation is simple: 1) Clean old flange 2) Replace bolts 3) Must use wax from old wax ring to get good seal 4) Place bead of sealant on original flange only 5) Stack as many extensions needed for desired height repeating step 3 6) Add wax ring 7) Bolt closet to floor.