These vintage conduit boxes (T37 Condulet) by Couse-Hinds have a solid copper body with a cast iron cover and rubber gasket. The 3 openings take 1" NPT. These were recovered from an outdoor lighting setup and you can see the original patina in photo #7 before I sandblasted and polished them. The original patina is pretty cool and I can leave them that way if you'd like. One side does have a hole that was drilled and tapped in order to mount them, but you can just fill it with silicone if you need to. Each one is a hefty 3.3 pounds.
The next to last photo shows that I also have the same thing in 3/4" NPT. The last photo shows it sitting next to a solid brass bracket, in case the copper color wasn't coming through in the other photos. I am willing to bet that there isn't another stash of these out there!