I've got some weatherproof outdoor junction boxes and am trying to figure out what type of connector is compatible with each hole/port. Below is a photo of a sample weatherproof box with two deep threaded "hubs(?)" on top and one on the bottom, and a shallow threaded hole on the back.

My understanding is that rigid/IMC threaded ends or rigid/IMC threaded fittings will fit in the deep threaded "hubs". What about EMT or liquidtite threaded fittings with locknuts? The deep hubs seem like they will not accommodate locknuts. Can one just leave out the locknut and thread an EMT/liquitite connector into the hub?

The shallow threaded hole in back looks like it should allow use of a locknut; is the threading correct for EMT/liquidtite connectors? Will rigid/IMC threading also work with that hole?

sample weatherproof junction box

  • 1
    All those fittings use the same threads....
    – Ecnerwal
    Commented Nov 19, 2022 at 13:02
  • My electrical box has 1/2" threaded hole. I have 3/4"copulers for running wiring inside plastic sleeving for outdoor use. Do they make an adapter for 1/2" male to 3/4' female so I can use 3/4" fittings or do you need to match the box and fittings? I chose 3/4" tubing and couplers for ease of pushing the wire through it however the box has 1/2" threaded hole. Is there such a coupler or do I have to return one or the other and either buy 1/2" couplers or a box with a 3/4" threaded hole? Thank you. Commented Mar 19 at 17:08

1 Answer 1


EMT connectors are permitted to be assembled into threaded entries of boxes, conduit bodies or internally threaded fittings that have tapered NPT threads. You do have to follow the box manufacturer's instructions, which I am certain say that you need to use some sort of thread sealant on all the exterior fittings for the box. Personally I use silicon sealant. You also need to make certain that at least three full threads engage with the box, and don't use the locknut in that situation. Of course everything you use with EMT outside needs to be rated for wet locations.

Don't use a locknut on the back. You can thread the same kind of connector in there. I believe you can also use a standard connection not rated for a wet location if the box is mounted on a wall, though I'm less certain about that. I've certainly done it and the inspector didn't complain, though I never actually looked up if it was acceptable.

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