Genuine Phonak Slim Tube Fit and go 4.0

Sound Delivery System 4.0 (SDS 4.0)  is the new acoustic coupling portfolio. Designed to support the Nathos Nova M NHS hearing aids, SDS 4.0 offers robust, reliable and comfortable acoustic coupling components.

These tubes are used on Phonak and Unitron hearing aids.
Left tubes are marked in blue and right tubes are marked in red, the length of your tube is the number