Coupling mobile member for synchronising two resonators, each including an interface pin periodically following a plane, closed trajectory, including grooves for holding the pins equidistant from an axis on a structure subjected to a torque about the axis, on which the grooves are coplanar grooves, radial with respect to the axis, for reception of the pins in symmetrical pairs with respect to a main, straight groove passing through the axis, in a plane perpendicular to the axis, and in which slides a main slide-block, which cooperates with a plurality of bars, each hinged on one side to one of the pins, and hinged on the other side to the main slide-block.