1. Remove existing aerator.
2. Insert disc into aerator with witches hat facing up and then the rubber washer.
3. Replace aerator.
1. Remove shower arm from back plate on wall.
2. Insert disc into shower arm (or hose), witches hat facing out, till some metal thread is showing.
(The rubber washer is not needed for shower installation)
3. Wind teflon tape around metal thread of wall pipe. Then screw on shower arm.