A barrel adjuster consists of two parts, an inner core and an outer part. The outer part has ribs to facilitate grabbing and rotating.
If the inner part can also be grabbed, turning the barrel adjuster requires the use of both hands. It may not be possible to grab, or even to see, the inner part. In that case friction will hold and stop it from turning against its end of the cable.
Barrel adjusters, for front/rear brakes and for front/rear derailleurs, are meant for fine-tuning. Given a standard way for fitting them on a cable, it is possible to adjust them—with one hand, without too much distraction, and while keeping one's eyes on the road—while cycling. (This requires that the barrel adjusters be installed within reach of the cyclist, rather than too far down near the frame, but their being within reach is the common place anyway.) For example, on a particularly long trip it is quite possible for the brakes to have finally lost enough material for the brake lever to become too close to the handlebar when squeezed. In that case the rider may well fine-tune the appropriate barrel adjuster while riding. Likewise, the appearance of rubbing against the front derailleur cage during a ride may be removed by a skilled cyclist by turning the FD barrel adjuster.
If the barrel adjusters are inline on a road bike, they will be more or less vertical. It is then easy to keep a mental note that rotating clockwise screws in the barrel adjuster, decreasing its length, and reducing the cable tension.
Can you first confirm that the four-point summary above is correct? Did I misunderstand anything?
Can you then confirm whether there is indeed, as I feel there must be, a convention for installing inline barrel adjusters such that the direction for screwing in or out is well established and can be performed without looking at each particular barrel adjuster?
This question is prompted by a video describing how to replace a barrel adjuster—as well as by my misfortune in having what appears to be a slipping connection between the lower part of the barrel adjuster and the cable, as if that connection was mistakenly greased at the factory. The presenter seems to know very well what he's doing, but then it appears that he installs the barrel adjuster in the wrong orientation, which complicates maintenance jobs on such a bike because the mechanic, at least the amateur one, will need to think about whether to rotate clockwise or counter-clockwise before every adjustment (which complicates maintenance on a stand, and pretty much precludes maintenance while riding).
Other Worthwhile Notes
- If adjusting from scratch, it is helpful if the two parts are screwed in as much as possible, because cables will not tighten themselves, only slacken.