I've got a bunch of 18awg thermostat wires that need to be spliced in tight spaces. Normally I'd use wago lever nuts because they can easily be installed and removed by others, but at 8.2mm thick they're way too big for the job. I'm looking for a 3 conductor tool-less splice kinda like this, except <4mm thick:

enter image description here

  • 1
    Even single conductor wire nut will be almost 4mm or bigger. If you remove tool-less then have a few more choices with climpers.
    – crip659
    Dec 23, 2022 at 17:23
  • @crip659 Yep crimping would be an easy solution to the space problem, but I assure you it really has to be tool-less. At the very least, removal has to be tool-less even if it's not reusable.
    – Navin
    Dec 23, 2022 at 17:26
  • 2
    Low voltage might get away with just twisting the wires together and taping them. Not recommended if under stress or high(120v) voltage. Your size limits do make it hard. Automotive connectors(thin ones) just might be at/under 4mm thick, but tools required for setup, not splicing/connecting.
    – crip659
    Dec 23, 2022 at 17:38
  • Solid or stranded?
    – bobflux
    Dec 23, 2022 at 20:56
  • Is there no way to move the splices to have more space? How do you even work in 4mm space?
    – crip659
    Dec 23, 2022 at 21:34

3 Answers 3


My go-to for that job is blue wire nuts e.g. Ideal 72B. I use hundreds when re-wiring fluorescent fixtures, which are all #18 wire internally.

If somebody told you wire nuts are bad, well I don't agree but they're just wrong when dealing with wires this small.

  • 1
    71Bs are slightly smaller than 72Bs, so if every mm truly counts, that's the choice. 72B goes up to 4 x 18 AWG compared with 71B 3 x 18 AWG but for this application that seems to be adequate. 72B 10mm diameter, 18mm long vs. 71B 8mm and 15mm. Dec 24, 2022 at 23:48
  • 1
    @manassehkatz yeah I use the blues a lot, they're easy to work with given 2-3 #18. I prefer to use nuts in the middle of their working range. Grays are a little tight for my tastes. If OP has an "every mm counts" situation they 're probably violating the box fill rules. Time for an extension box. Dec 25, 2022 at 2:07

I think the best you can do with Ideal brand wire nuts is the 71B:

  • Holds various combinations, including 3 x 18 AWG.
  • 8mm diameter at the base - tapers slightly to the top.
  • 15mm tall

So not quite as small as you'd like. Hard to compare with Wago as I am having trouble finding documentation of the exact dimensions.


the best tool-less splice I could find was Wago 2273-203 which is 5.8mm thick.

image from Wago web site

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