The top tube/ring assembly has the bottom ring flush with the low end of the tube.
The upper ring is recessed 1 11/16" below the top end of the tube.
The instructions have you apply a glue ring and slide the centering ring in position. Good luck with that, the ring will spin and probably end up crooked in the tube.
I applied the glue ring using the top edge of a dowel.
Notice the tape ring set at 1 11/16" from the top.
Apply a ring of glue around the top of the dowel.
Use the tape ring as a depth guide as you roll the ring of glue onto the inside of the tube.
Used the flat end of a ruler to push the ring into position.
Used the flat end of a ruler to push the ring into position.
The square end of the ruler helps keep the ring flat as it is slid into the glue.
Check around the perimeter of the ring making sure it is flat and the same distance from the top of the tube.
You can apply a glue fillet using small glue drops applied using a Q-tip.