These Friction Stays open fully to the corner of the window, after the operation of a release catch the opener can be slid across to allow the cleaning of the outer pane from the inside of the room.
These items are supplied in pairs and the price on the site is for a pair.
They can be purchased in various lengths and stack heights.
The length is self explanatory
The Stack Height is the distance between the two outerparallel surfaces, one of which contacts the frame and the opposite contacts the opening sash (the thickness)