273 adjustable rocker conundrum..

Almost positive the thread 'interference' in the original design was in the adjuster, not the rocker. The adjuster was hollow, & slightly oversize. When screwed into the rocker, the adjuster thread was able to 'compress' slightly because of the hollow centre. This kept the adjuster tight enough to stop it changing position. The thread in the rocker may well be a standard 3/8" NF thread, in which case adjusters with a locknut are probably available.