Originally Posted by
smd4
No they don't. I used to have notches on the cable adjusters on my brakes. then I got new cable adjusters without them. The cable doesn't move on its own, because no amount of cable force will "push" the adjuster screw into the brake arm. Doesn't even look like Shimano installed them on the earliest Dura Ace RDs. I suppose it's possible, though highly unlikely, that vibration could cause the screw to move...
I responded to your statement rhat they don't prevent rotation. That's different than saying they're unnecessary. Had you said the latter I wouldn't have responded.
In any case, adjusters and similar applications do move over time and adding something to prevent that is SOP.
If we follow your logic, we'd never have problems with screws getting loose, and Locktite wouldn’t exist.