This is the union, repair folks have asked for- Screws into the pump, and it transitions into the 2" glue on Pipe Fitting.   Usually found on top of pumps, but I've seen them used in many applications.
Thread to Thread they are 3"  across.  I have personally used on Praher and Swimmables  High temp
unions.  There are some different brands out there, I have not tried all of them.