There were a number of set screwed upper stacks that all have gone by the wayside long ago, back in the later 1980s and early 1990s when threaded 1" steerers were the standard. Steerer thread damage, headset race/lock nut set screws stripping out being two "common" issues with them. An assembly mistake I've seen was to not fully tightening the race and lock nut against each other, before employing the set screws. I have to admit not liking them but I never rode my MtB like people today do and am small/light. Andy.