is also formed moreover the fixed element supports a pin 80 to which the arm 7 and in particular a first or lower end 70 thereof is pivotally connected besides to the fixed element 8 the opening closing means 6 comprise a movable element 9 slidable on the fixed element 8 and integral with the rod 5 so as to be driven thereby in a translation with respect to the fixed element the movable element 9 is precisely engaged without clearances in the aperture 50 by means of coupling teeth 90 a 90 b besides being engaged with the fixed element the lower end 70 of the arm is linked with the movable element in particular on the movable element 9 a slot 91 is formed having a vertical or longitudinal 91 a straight segment arranged parallel to the axis x u2032 and thus according to the sliding direction of the rod 5 from at least one of the ends of the vertical straight segment at least one horizontal diverging segment 91 b extends preferably a straight or transversal segment thus arranged orthogonally with respect to the axis x u2032 which is joined with the longitudinal straight segment via a bend 91 c in the described example there are two transversal straight segments so that the slot is c shaped with the concavity facing towards the inside of the room environment and thus opposite with respect to the opening side of the hung sash a peg 71 of the arm is slidably and rotatably engaged in the slot 91 the peg projects from the arm 7 at the lower end 70 thereof in proximity and beneath the pin 80 with reference to fig6 the slot 91 and the pin 80 are at positions that are both transversely.