Abstract: A window frame, especially for ventilation by setting at various angles a plurality of slats mounted on said frame is disclosed, the improvement consisting in that the control lever which acts upon the rod which gangs the slats for setting them at an angle together has the end pointing towards the interior of the frame in the form of a scalloped sector, the points of which engage, in turn, a notch formed on a brace which is removably fastened to the window frame upright. The mechanism is reliable and versatile since it permits that the slats may be set at various angles in a stable manner. Means are also provided for preventing slat rattle by properly shaping the individual frames of the slat carriers. Thermoplastics materials are widely used in the construction of the frame and accessories.