Abstract: An arm (2) on which to mount an extractor and other equipment, the arm (2) is hinged by its inner end (9) to a support (17) with the intermediary of a mounting bracket (14), so as to be allowed to pivot essentially in the horizontal plane. A retaining device (18) acts between the arm (2) and the mounting bracket (14) to retain the arm in the set pivotal position. The retaining device (18) includes a rod (24) which carries friction washers (23) and which may be actuated by an actuator (20) via a rotationally mounted yoke (38) in order to move the friction washers (23) from their retaining frictional engagement with a plate (34) connected to the mounting bracket (14) and thereby allow the arm (2) to be pivoted as desired. The power actuator (20) is remote-controlled by a control unit positioned on the extraction hood of the extractor.