The top and bottom rails are made of silver-painted aluminum and measure 20mm x 20mm. The pleats are 20mm wide. The enclosed 4 pieces of plastic carriers are adjustable for frame thicknesses from 15mm to 24mm. Quality: 2. Darkening: The special coating with the light-stopping back (silver) has a darkening function. Ideal for bedrooms or children's rooms. Measuring/Size range: How to measure correctly: Please only use fixed measuring tapes, e.g. a folding rule. The width and height measured by you are also the order size. Measuring/Installation options: Klemmfix installation: Pleated blind installation is very easy and practical! With the enclosed adhesive/ clamping carriers, the pleated blind system is mounted directly on the window sash (frame thickness 15-24mm) without drilling or screws.