Since the R-5070 picture was posted, I thought I'd post this one. It is marked R-5071, and has a hole all the way through it (no threads). It certainly seems to be a large bushing or wall tube, for passing power through the wall of a building. I have no idea where it came from (I found it at an antique shop in California).

It is interesting how similar the shape is to the R-5070, although the use would seem to be completely different...