This is a concealed non-releasable restrictor designed to restrict a upvc door/window.
The restrictor has 2 friction screws on the plastic slider that can be tightened to increase friction as the door/window is opened and closed.
The restrictor will stop the door/window at an angle determined by exactly where the restrictor is fitted.
The width of the track (the part where the plastic slider slides)is 18mm.
The only way to release the restrictor is to remove the fixing screws.
The item is unhanded. They are sold singly, the price is for one.