Abstract: A window stay assembly for fitment between a window frame member and a window sash member and having two preferably elongate window stays extending directly or indirectly between the window frame member and the window sash member. Those ends pivotably mounted preferably through a mounting plate to preferably the window frame member directly or indirectly interengaged by direct or indirect gearing so that the movement of one gives rise to some predetermined proportional or identical movement of the other. The distal ends of the window stays are themselves pivotably mounted directly or indirectly to the window sash member with at least on of the pivotal mounts being through a friction slide mechanism. The arrangement enables a reproducible opening of a window from its frame using a thin window stay assembly.