I have this debate regularly with facilities where I find “short-threading” on their flanges/manways, etc. This phrase is from an old pipe-fitters manual, and it’s what I was taught in 1993 when I entered the chemical process industry and PSM/RMP covered processes. Today, “full engagement” is defined at the bolt/nut being FLUSH. So I asked the all-expert in everything Process Safety (sarcasm) “AI” about the “three-threads showing” and believe it or not, it responded with the following: