Looks like their 'two way' rods have a captured nut, so they will adjust in both directions. I believe that is the same as the Martin design.
With their 'dual action' truss rod, the rod that the adjusting nut is attached to turns when you adjust it. Some of this type have left-hand threads on one end, and some have a finer thread pitch. The ones with the fine/coarse threads adjust much more slowly, and are easier to fine-tune when adjusting neck relief.
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