This is how I put them in. I turn the offset in the tube to one side of the sight base then insert the end of the tube through the ring, barrel nut and spring into the hole in the upper. Usually they are not in perfect alignment and it will be easier with the offset turned to one side of the sight base than it will the other side of the base. I try each side to see which is best. On occasion it takes a light flexing of the tube to get the end into the upper. Flexing NOT BENDING of the tube. After it goes in I roll the tube down 90 degrees and atttempt to slide the other end into the base. This is when you really see how well it was aligned. If it does not go staight back into the hole in the sight base it is out of alignment and it is time to adjust the barrel nut.