A conversation on the Facebook group gives me the opportunity for a new tutorial: double double stitch!
A double double stitch is used to obtain a stronger bow than usual. It is particularly recommended for very long chains because there is less deformation.
The goal is to get a knot at 4 feet instead of 2.
During the first part of the stitch, before tightening the knot, return the shuttle in the loop in the direction indicated by the red arrow.
Then do the second part of the knot. Likewise, you must pass again the shuttle in the loop in the direction indicated by the red arrow.