What swim jet fitting is this?

Welcome to TFP.

Maybe @1poolman1 is old enough to have an idea.

squampool said:

Previous owners covered this with a sheet of vinyl and filled one in with calk. I’m on a mission to fix it. However, I scoured the Internet, looking for six screw return fittings and couldn’t find anything. They could be pretty old. Also, the inner part is cracked so I’m going to see if I can replace it

The outer dark ring is 8 inches in diameter. The inner jet is 1.5 inches.

Thanks in Advance!

Click to expand...

The fittings and the "six-screw" pieces are separate. Those appear to be Waterway spa jets. The missing piece is a trim ring, probably chrome-plated plastic that the spa manufacturer used to make it pretty. Have never seen the trim screwed into the vessel, they usually are press fit or bayonetted onto the jet. May have to contact the spa manufacturer to find what they used.
As old as that spa appears, it was probably built at a time when "everybody" thought they could manufacture a spa shell, throw some equipment into it, sometimes special order, and go broke two years later. It has taken decades for there to be at least some "normal standard" in spa and spa equipment manufacturers. Then you run into Sundance or old Jacuzzi and its DC system.