This product allows you to use your caravan awning in a box awning.
First, you thread an adapter strip with both 4mm & 6mm beading into the box awning, and on that, you attach double-sided plastic rails, which makes it possible to attach an awning with 9mm beading.
3 m = 4 double-sided plastic rails
4 m = 6 double-sided plastic rails
5 m = 7 double-sided plastic rails
You can find the plastic rails here - Double-sided plastic rail