This is what I installed for the pop off relief valve
You can find it cheaper, just have to do some searches.
I decided to replace mine while I was working on my air system. I could not get this to come out and ultimately broke it off. Had to use a saber saw to cut slots in the portion left in the tank and use chisel to get it out and had to chase the threads to put the new piece in.
All the parts that I replaced had numbers stamped in them so if you remove and look closely you can find the parts you are looking for. In some cases I removed the part, got the number, then reinstalled until I got the new part.