The aim of the invention is to provide a simple and secure fixation of a mounting comprising arms (1a, 1b) hinged to a rotational body (1) for adjusting the angle of the arms relative to each other and for holding an instrument (7) in a stable manner. This is achieved in that the adjusted angle can be fixed by a ratchet (3) attached to the rotational body (1) via a coupling (2), the coupling (2) is equipped with a switch (5) which locks the angular position of the arms (1a, 1b) relative to each other in a switch position, and a locking device (4) is provided for connecting the ratchet (3) to the coupling (2).
