An adapter for mounting a support device for a stringed instrument, such as a violin or a viola. The adapter may include a first bracket having an area for at least partially encircling the tailpiece button of the stringed instrument, a second bracket, and a connecting device. The first bracket and the second bracket are disposed and connected by the connecting device in such a way that the area of the first bracket at least partially encircling the tailpiece button is in stationary contact with the tailpiece button.