The opening in a window casing assembled from four lengths of extruded aluminium channel is provided with two sliding sashes having frames of extruded aluminum. The lower horizontal frame member of one sash rides on wheels whose rim matches the semicylindrical top face of a guide rail on the lower horizontal casing member so that the sash may be pivoted about the axis of curvature of the guide rail face. Tilting of the sash is limited by brackets, each bracket including a slide guided along the upper casing member and a link pivotally connecting the slide to the top of the sash. When the sash is locked in the plane of the casing, sealing strips on the sash cooperate with sealing surfaces on the casing above the pivot axis while the engaged sealing strip is kept straight by abutting engagement of respective abutment faces on the lower casing member and the sash below the pivot axis.
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