All three fittings on this tee are the same. The knurled thing for the left one has been moved up the line out of frame. I need to remove this line from the tee without damaging the tee or the other lines. I tried squeezing it with pliers and twisting while pulling on the other end, but no sign it moved. I hope it’s not glued on. Whether glued or not, I don’t see any reason for the knurled outer ring.
It’s in a 2003 RV, and it is probably original, i.e., eighteen years old.