groove 21 and continuing at its ends into transverse grooves 24 and 25 respectively opening into the environment fig3 and 4 illustrate a locking means in the shape of a turnable member consisting of a turnable shaft 26 supporting a hand wheel 27 at one of its ends and a catch at the opposite one by turning the hand wheel 27 the catch 28 may be moved from a retracted position inside a slit 29 downwards into a blocking position behind the guide bushing 8 in accordance with prior art technology the casement 1 may be pivoted relatively to the frame 2 in the manner illustrated in fig2 by continuous as well as dash and dot lines in accordance with the invention the pivotment of the casement 1 may continue in the direction of arrow 30 to position the casement 1 in the frame 2 while the guide bushing 8 is being guided in the transverse groove 24 in this position of reversion over 180 u00b0 it is now possible to both lock the casement 1 in the conventional manner by means of a locking fitting not illustrated at its one end and also to secure it by means of the turnable means 26 27 28 at its opposite end from this position it is possible in accordance with the invention to pivot the casement 1 following turning of the turnable member to release position outwardly in the same direction as previously or to pivot the casement backwards in the opposite direction owing to the design of the casement.