These domes are suitable for the Phonak speaker 4.0. This speaker is used with the Unitron D Moxi series.
How do you replace a dome of a Unitron or Phonak hearing aid? Hold the thin tube between your thumb and index finger with one hand. With your other hand you pull the dome off. Then you take a new dome and press it on the thintube. Don't forget to push the whole thing down with your thumb.