projections 1b referring to fig2 there is seen an exploded view of the embodiment casement window frame shown in fig1 the locking tenon 3a is engageable with a mating member 6a which secured to a casement 5 by a screw 4 the slider bar 3 and locking tenon 3a are movable along the length of reinforcement piece 2 in the direction indicated by the arrow the slider bar 3 and locking tenon 3a thereby cause tilting and turning of casement 5 as is well known in the art the slider bar 3 of the tilt turn mechanism runs below the cross leg 2a of the reinforcement section 2 but within the h shaped support section 1c the locking tenon 3a of the tilt turn mechanism projects from the slider bar 3 into a mortise 2b or lengthwise recess of the reinforcement section 2 a fastening device 4 which may be for example a screw fastens reinforcement section 2 and casement section 1 if sliding bar 3 moves below the cross leg 2a of the reinforcement section 2 the locking tenon 3a attached to the sliding bar 3 and the tilt turn mechanism of the window frame are shifted either into the active or the rest position the window frame of the present invention has the necessary strength and is assembled in a simple manner with all of the desirable and required features of such a window naturally the invention is not limited to the embodiment casement window frame consisting of plastic hollow sections as described above the invention may also be successfully used in window frames.