I have seen many instances of the metal clevises wearing the threads off the rod and failing, both on 2-56 and 4-40 but more 4-40's on big gassers., I always lock the clevisis into position after getting the trims set. I usually just use a good grade epoxy instead of thread locker, seems to work okay. I've never had a plastic clevis wear out the threads on rod but I have seen a hard landing (i.e. crash) strip them.