[MikeK]

Self-locking really means that they do not ever lock. There is friction/ interference in the thread fit making them stiff to turn, somewhat like a 'self-locking' nut. The supposed advantage is easier adjustment, as you need two thin tappet wrenches, not three.

Some guys do OK with them, others, including me, have found that a significant number of them (maybe 1 or 2 in a set) do not hold all that well. Fixes for this include running the thread way up, pin punching the threads to increase interference, blasting the threads with carb cleaner then compressed air to de-grease and applying locktite blue before running them back down to correct adjustment.