Solar Powered,
You bring up an excellent point about the threads on U.S. electrical equipment.
Most U.S. electrical equipment, hubs, connectors, EMT, rigid, IMT and conduit and fittings use what are called straight NPSM threads. These threads are known not to be reliably watertight at even slight positive pressure without the addition of thread sealant.
The NEC requires explosion proof equipment and conduits for classified locations such as, fuel pumps, to use tapered NPT threads like plumbers and gas pipe fitters use. NPT threads compress and lock together when tightened, so they are water and vapor tight and are also resistant to loosening from vibration.
Whenever I have to work with pipe, I always carry both types of dies in my threader kit, because once you get out of that classified location you can go back to using the factory NPSM threads that come on our rigid conduit.
As an example, this is why when you try to use a 3-foot long piece of 1/2 rigid pipe from the hardware store to make an extension pole for a ceiling fan, it does not thread properly into the fans hub. The fan hub in NPSM and the pipe is NPT.
Something that everyone has probably tried at one time or another in a pinch.
