A friction supported stay comprising a track (10) secured vertically to a window frame with a slider (15) connected by link (18) to a strut (16) in turn connected to bar (24) which is also connected to slider (15) by a link (21). The bar, which is normally connected to the window has a nose member (35) which engages in a plastic, shaped cap member (14). The cap member (14) has internal cam surfaces (36) (37) which are asymmetrically disposed with respect to the central longitudinal axis of the track. One cam surface is at a greater angle to the axis than the other. The corresponding surfaces of the nose portion (35) of strut (24) are similarly inclined to each other and to the axis of strut (24).