OK, we gave that away in the prelude to the questions. RMC is Rigid
Metallic Conduit. You can thread it, which means you can use it as a bonding
path and you can seal it [344.2]. You can use metallic tubing as a bonding path,
but you have to jumper around the connections to ensure integrity. Obviously,
you cannot use nonmetallic raceway as a bonding path.
344 lists four uses [344.10]. These four actually encompass a tremendous range
of applications. But don't make the mistake of considering RMC your only conduit
option; IMC  is a thinner-walled metallic conduit that may be more
appropriate for your application, plus there are nonmetallic conduits. IMC and
RMC have their own "Uses Permitted," and though they can overlap
it's not the case that you choose RMC over IMC just because you want more "Lift
truck withstand capability" than RMC provides.
You can use RMC and IMC in all atmospheric conditions and occupancies, corrosion
environments, cinder fill, and wet locations.
doesn't list any prohibited uses. However, avoid introducing dissimilar metals
into the RMC system [344.14].
bushings, couplings, connectors, brackets, etc., listed for use with RMC.
Article 344 doesn't explicitly state this, but the listing requirement is a
general requirement provided elsewhere in the Code.
You can't, for example, use
connectors designed for use with plumbing systems. Nor can you run a length of
PVC in an RMC system (you can connect a PVC system to an RMC system, typically
the case where conductors are run underground in PVC to stubs that then mate
with RMC; be careful to bond the grounding/bonding wires (run inside the PVC) to
the IMC so there aren't differences of potential.
Do NOT use IMC fittings with RMC, despite their similar appearance and identical
use running threads on conduit for connection at couplings [344.42(B)].
Amazingly, the NEC does not define "running threads." So what does this mean?
What you're supposed to do is thread the conduit and then screw on one fitting.
Then you screw threaded conduit into the other end of the fitting. The completed
assembly should not have much unused thread left over on either end of the
What the NEC does not want you to do is stretch the threads twice; that violates
the basic principle of fastening things together by tightening to the elastic
limit one time and results in a mechanically compromised connection.
With running threads, you create a long threading area on conduit piece #1. Then
you run the connector up that piece until it's no longer over the end of the
stick. Now you can mate piece #1 to piece #2 and spin the connector halfway onto
piece #2. This overcomes the problem of trying to spin the second piece if space
to do so is tight. But it results in a compromised installation that, among
other things, ruins the ability of the conduit to serve as an equipment
grounding conductor. And normal vibration will eventually cause that connector
to move completely off of that second piece some day.