QUICK RELEASE holder for bicycle seats. average hole for holder: 15mm minimum frame diameter: 26mm maximum frame diameter: 35mm Installation: 1. Attach the holder to the bike frame using a wrench. 2. If the handle is too loose, select the appropriate size of the spacer (the set includes 3 sizes from 26 to 35 mm-standard). 3. Insert the arch mounted on the car seat into the holder on the frame. 4. Secure the arch by pressing the safety slider. 5. Mount it above the luggage compartment (1.5 to 2 cm) to achieve optimal suspension. weight: 300g