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I installed a fancy light fixture in a US single wall box, and had a terrible time with the mount and trim until I tapped out the fixture's mounting caps with a 8-24 tap and replaced the mounting screws with my own cut-to-size 8-24 bolts.

enter image description here

Looking back, my box has normal mounting lugs at 2-3/4" (69.85mm?), but the fixture's plate has its mounting rings a little narrower at maybe 2-9/16 (60mm?) and I had to force the box screws in a bit crooked.

I think when I threaded the mounting screws into my bolt-cutter/wirestripper to cut them to length, it formed the thread to 8-32 to make them not quite match the knurl knob, which made it much harder to thread onto the stub and made the matching the proper length much more awkward.

The whole job took 10x as long as normal with all the fiddling around with everything not quite right.

So, what are the non-US standard box lug spacings and mounting screw threads? (With US spacings being 2-3/4" with #8-32 threads)

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    Was the source of this fancy lamp a US bricks-and-mortar retail store (even if their mail-order arm)? Or was it a primarily mail-order outfit of some kind? Were the wire colors blue and brown? Was the ground yellow with green stripes? Jul 26 '20 at 3:23
  • I've seen M4 in some UK gear, but I don't know if these fittings would necessarily expect a box to be mounted to. Jul 26 '20 at 12:09
  • @Harper-ReinstateMonica -- it was mail-order, the wire colors wer black and white.
    – Dave X
    Jul 27 '20 at 4:29
  • @SomeoneSomewhereSupportsMonica -- Besides the buggered-up threads, the mounting plate was a problem--none of the slots matched the US holes. I found 60mm and M3.5 dimensions on a diagram for a European wall box.
    – Dave X
    Jul 27 '20 at 4:35
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On http://internationalconfig.com/icc6.asp?item=72350-F I found this diagram with M3.5 lugs spaced at 60mm, which matches the mounting plate/mounting strap packaged with the fixture with its inner 60mm rings.

An M3.5 thread is a 3.5mm OD by 0.7mm pitch thread, while an #8-32 thread is 0.164" (4.156mm) with a 1/32" (0.794mm) pitch. A #6-32 thread is 0.136" (3.45mm) with 1/32" (0.793mm) pitch. They don't quite match, but visually they look close.

enter image description here

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    Thanks for doing the research and sharing your answer. Be sure to give yourself a check mark as soon as the system will allow it!
    – FreeMan
    Jul 27 '20 at 11:32

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