Clamps are used to secure tray elements to the existing tower attachments. There are two types of clamps: Fix clamps with a defined compensation hight and variable clamps that can adjust to different heights.
There are clamps with fixed bolts and clamps for loose bolting.
Clamps with fixed bolts have to be prepared for the right thickness of tower attachments. A sign / marking at the bolt shows the position of the clamp. So you can fix the clamp from top.