There are three things to consider. To install the backrest, you position the tab that gets screwed down. at the bottom center of the backrest is a slot that must be postioned BEFORE pushing in the top two posts. I had installed my correctly when I installed my GIVI box. After my 6000 mile service, it would not stay in. Even with the screw installed if you push up on the bottom and get the slotted part in you just pust the two top posts in and it will stay. You don't have to use glue unless your backrest is damaged.