Abstract: Mechanism for stepwise adjustment of the distance between a primary element, attached to one part of a chair, and a secondary element attached to another part, characterized by: (a) two stop slides mounted on the primary element to slide in the direction perpendicular to the adjustment direction, between an opening position and a locking position, (b) a number of stop recesses in each stop slide, one above another in the adjustment direction, placed on a first side of each stop slide which faces the other stop slide, and open to the first side, with the stop recesses of the two stop slides lying opposite one another in pairs, (c) an elastic element for pushing the stop slides into the locking position, (d) a bolt passing between the stop slides, perpendicular to the adjustment direction and to the direction of displacement of the stop slides attached to the secondary element, and (e) a spreader mechanism with a mover mounted on the primary element such that it can be shifted parallel to the adjustment directi