Keder is the brand name and also the common name for the premium awning bead sewn onto the edge of vintage trailer and other awnings when attaching to a trailer awning rail.
The Keder wrapped welt we sell (VTS-980) is 8.5mm diameter and has a single flap 20mm wide for sewing. That's a easy modern way to attach a bead on the edge of your fabric. But for a truly authentic look, you'll want to wrap your fabric all the way around the bead. If that old school look is what you are going for, use this version without the flap. It's simply the same extruded PVC flexible cord or "rope" but without the polyester wraparound flap. When you wrap your own fabric around it, you will have the proper diameter for standard travel trailer awning rails.
Priced and sold by the yard.