The gauge is called a magnahelic. It’s just a pressure gauge I have on the return to give me an indication of how much total airflow I have.
The threaded rod is 3/8, and the greenish square thing is just a really thick washer. They sell that channel, along with a bunch of different hardware bits that go with the channel (including the green square washer) so you can build racks and mount things. They have it at our local Home Depot but not sure if they are in every one. If I remember, it was sort of near the electrical supplies.
Does that help?
Thanks
Scott
FFDE36CA-5063-4E5F-A12E-76E9E256DF1A.jpg