I added in an Inline Barrel Adjuster on one of my bikes. It uses an old Campy Tourney derailleur, it is quite picky, I often change out wheel sets and need to make adjustments. I am at the point that when I change out the wheel set I just make a few twists to the adjuster and I am in the sweet spots. On another bike I added a barrel adjuster to the boss at the wheel stay. Note that all my adjustments are very small. If you need big adjustment then something is wrong...