Question about Fischer Xtreme II

Hello, as far as I know, there are several types of fixing system used by all manufacturers.
This roof box has a sort of clamp that is tightened from the inside of the box.

Good evening. Good evening. Not the same thing. The principle is the same but the fixing system is not.
You need to know that the box opens on both sides, which makes fixing easier.
The fixing strips are made to standard measurements. Neither too small nor too large.