Most windows in Germany are of the turn/tilt type, which allows for a constant ventilation in the tilt position. However, the bed room window in my apartment is just a simple turn type window. I therefore needed a way to secure the window in a slightly opened position, e.g., to provide ventilation over night. The solution I came up with is based on a rotating wedge that presses against the underside of the window and keeps it firmly in place. The wedge can be operated with one hand allowing for an easy adjustment. The design is 3D printable. If you want to print your own version of this window stopper you’ll find a detailed description of it in my book on Mastering OpenSCAD.