I never got into poe and didn't have as much time in d2 as you, but I played the crap out of d2 original. I also couldn't stand d3. What a disappointment.
I really enjoy d4. I was not going to buy it but a friend who I often agree with on game choices did and was looking for someone to play with so I joined. No regrets. It feels like a modern Diablo game to me. Cross platform works well, which is nice so we can play with another friend who was obsessed with d2 but became a console gamer over the years.
I am a lot busier than I was when d2 came out so I only have a single character, around level 60, but I'm looking forward to the first season.
Unfortunately threaded racks can be lots of different sizes - the most common in my experience are 10-32, 12-24 or M6x1. I just label racks with their screw size in a visible area to avoid confusion.
Someone at my current job ruined every single thread in one of the server rooms, so that's definitely a possibility as well. I will say it is obvious when someone has done that once you take a close look, though.
Best bet is to just buy one of each screw size at a local hardware store and try them out. Maybe also see if there is a model number on the rack, but don't hold your breath.