One of the tubes is made by Solarforce, the second tube does not have an ID. The second tube will screw into the SolarForce tube, but the Solaforce end caps with finger loop will not screw onto the no-ID tube, they will only screw into the Solarforce tube. The end caps threads bind on the no-ID tube threads because it looks like the thread peaks of the end caps bind in the bottom of the threads of the no-ID tube.