If you have built a Borealis rocket, with those lovely thin tubes separating the 2 fuselage sections, you will want this

My Borealis flew fine, but those thin paper/card tubes just didn't last. I replaced mine with brass tubing and designed this to replace the upper fuselage. In time I will redo the whole rocket in plastic. This replaces the top tube which tends to crumple in a hard landing.