Ham Radio Operators may appreciate this:

This is a very simple print which I designed because I needed to put a UHF/SO-239 barrel through the wall of my metal trailer. The trouble is that the trailer has a lot of electronics in it, some of which seem to be noisy (probably the solar charge controller in particular). When the barrel was in contact with the skin of the trailer it introduced a huge amount of RF noise into the signal, so what I needed was a way to put the barrel through the wall without it touching any of the skin of the trailer. (I found that a coax through the window didn't pick up any noise at all, and all a barrel is is a short piece of oddly designed coax =])

Anyway, the pictures should make it clear how this works; you might need to adjust the diameter for your printer to get it tight enough. I like to have it tight enough that I have to thread it on, but I didn't try to make it tight enough that I didn't need the metal nut on it as well, since that made it too difficult to work with. You can easily adjust the variables in the scad file to get what you need. If someone feels it would be useful I could easily make this a customizer thing.

Print Settings

Notes:

The main thing I'd do is make sure that the shell is solid; it's 2mm thick, so if you aren't careful you could have infill in there and that will likely not be a good thing.