Hi!
Is it a bug or not?! It seems to me that they work in reverse…
See gif 
Thank you
It goes so quickly I can’t tell which tool you are using but Outer Shell and Union really do two different things. Outer Shell only keeps the outer surfaces of the objects and throws away everything else. Union just joins the two objects.
I see they do appear to be inverted in SketchUp Go. @colin, can you relay this to somone who can fix it?
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I can reproduce it in SU 2021. It might be the same in SU2024 (I can’t test it ). So, it might be a general bug…
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So it is in SketchUp 2024, too. The native Solid Tools and Outer Shell create other problems for my workflow so I never use them and hadn’t noticed.
Looks like the names and toolbar icons need to be swapped.
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The models I make myself don’t behave. Both outer shell and union leave me with the same results.
Could one of you add the model you are using?
works fine on mac…
I’m working on a manual about SketchUp Free, SketchUp for Schools and SketchUp Go… I don’t know what to write now haha 
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Here you go Colin. Did you include the inner void when you made a group/component of the outer box?
Union Outer Shell.skp (51.4 KB)
@ateliernab try it with my model.
Fortunately the exact situation doesn’t seem to come up that often. Yours is the first time I’ve seen this report since the Solid Tools were introduced more than a decade ago.
FWIW, I wouldn’t think to use either of those tools to model the exact object in your example.
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works fine aswell in the web version for me…
Well, testing with Ruby code, is similar result with this model:
test_unio_os.skp (31.9 KB)
@colin ?
So I wonder what’s in the code with SketchUp Go that makes the behavior different on Mac and Windows.
these solids do not have a void inside (each one). Maybe this is the point… if the void part is present at the beginnig or become afer the operation
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that’s odd. with your model it’s reversed.
after re checking, it changes when the void is already inside or not.
if the operation creates a void, then it’s fine.
but if the void is already there, then it’s reversed.
edit : I never noticed, most of the time I use eneroth’s solid tools. native ones are mostly used for demos / classes, and for that I use the exemple I used above. the one that works
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So then maybe it’s more than just swapping the toolbar buttons.
Like you I use Eneroth Solid Tools or Bool Tools 2, never the native Solid Tools.
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At a glance, the model I made and the one Dave made are the same. Not going to worry too much why my one doesn’t work!
I see the two operations reversed on Mac desktop, Mac web, and Windows desktop and web. I didn’t find a case where they are not reversed. Even iPad has them reversed.
I will check if it’s a known issue.
My guess is you didn’t include the inner void when you made the group for the box. I did that initially, too. Then I fixed it.
I don’t know how big of a problem it would be but it seems like swapping the buttons and the popup tool tips should be low hanging fruit.
it’s not a matter of version / OS but of geometry.
try my file. the operations work as planned.
test nab.skp (124.0 KB)
ok, new problem here.
First set is the standard outer shell. it works.
then I do union by clicking the top first. it does outer shell. then I do union by clicking the bottom first. it does union. then I redo union by clicking the top first. it goes back to outer shell
it’s super inconsistent. If I decide to use union on the 3 sets, top then bottom. sometime it works. sometime it doesnt. same with bottom then top.
it’s always 2 one type and the 3rd another type
this is 9 identical copies. and you see the result of 9 identical unions, top then bottom group.
looks like Union works all the time 50% of the time.
That one behaves on Windows, but on Mac both tools give the same results, but just in web.
I will ask the web team to take a look.
my file above was not made in the web version but in the latest desktop one.
it’s a bit of a heads or tail tool I guess.