20155 (labeled 24) is the compression adjuster and 20156 (labeled 25) is the Rebound Adjuster.
From closed, the Compression adjuster has 3.5 turns to fully open.
The rebound adjuster has 4.5 from its fully closed position.
The thread pitches are different. If you start with both the compression and rebound closed and open them together by opening the compression adjuster, both will be fully open at 3.5 turns of the compression adjuster. When closing both to the fully closed position, it is best to start by closing both together until you feel a valve bottom out. DO NOT force the adjusters at this point as excessive force can dislodge the press fit valve retainers. Once you feel one of the valves closing ,open the rebound valve slightly and see if the compression valve can be further closed. Repeat until you are certain the compression valve has shouldered out and the close the rebound adjuster.
Adjustment is best made using a small Allen key in the adjuster holes.