I have come across steel versions of those with electrical conduit, specifically around explosion proof and rugged/environmental boxes and fittings. Hope that helps.
Are they npt? They look like conduit bushings but those are a straight thread. If they're npt I'd like a source as well
Found this link on google: http://www.plumbingsupply.com/brass.html About half way down, they are called face/flush bushing, but limited selection of sizes
Badsco is correct face or flush bushings npt can be found at any good plumbing supply these look like brass but are available in many types of materials
That's the right idea but the wrong size...I need 1/2" NPT to 1/8" NPT and 3/8" NPT to 1/8" NPT. At least I now know what they're called.
Those sizes may be tough to find; as a worst-case, you could get solid brass plugs and drill/tap them for the 1/8" fittings. What you'll usually find in these sizes is ones with a hex head to allow tightening the outside thread separately. Trying to use the 1/8" to tighten both will usually result in a stripped 1/8" thread. I've used the hex-head types, installed them, then cut/ground the hex off. You might have to tap the 1/8" a bit deeper after doing this.
you can get allen socket head brass pipe plugs.these will have the advantage of centering the hole that you drill thru the center.