How can I select only the recessed areas of an object?

Hi all,
I have a metal part, and I want to assign a different material to the recessed areas of that part, so that the outside has a polished metal finish, and the recessed area has an unpolished/rough finish.
The model was made in Rhino and imported as an fbx. it has lots of polys and tiny filleted edges.
How can I do that?
Going in edit mode and brushing the polys is incredibly tedious. Surely there is a better way of doing this?
I can’t seem to make the “select similar area” method work. I lower the threshold and Blender still selects polys that are way out of my selected area. I don’t get it.
Is there a way that you can use another object as a brush?
Thanks for your advice
Here’s a screenshot of the part to better understand

Lots of ways.

heres one way, select by area, select one face you want, then adjust threshhold.

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Thanks but I forgot to mention that the object was made in Rhino and imported as an fbx.
It has lots of polys and filleted edges, and I cannot make the select similar method work.

Upload yr mesh if you can, Ill see if I can find a way?

You could use decimate planar to tidy it up a bit?

You could also use a material ‘trick’ with AO, or a spherical gradient to get to the edges/recesses

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Thanks a lot.
Here’s the link to the file (35Mb)
Really eager to see how this can be done.
I know that making it straight in Blender would make the selecting easier, but it’s just an example model for me to understand I can do the selecting for some other models I am making in Rhino.

Yes ambient occlusion looks interesting (a little technical though since I’m a beginner) but the material between the polished surface and the unpolished recess should still be different.
I’d really like to find out how I can do the selecting.

Ok, so its quite a messy mesh, but whole parts are slightly separate.

Use the l key in edit mode to select (l)inked verts / welded verts.
You can the use h to hide these parts.

Some degree of organisation is going to be needed though, other methods maybe faster. (depending on what you need this for)

The bevels are really messy, so if it doesnt matter much you would be better off just copying one of them and texturing it, then radial array as instances.

You could also try an attribute transfer from a similar low poly blender built mesh, and transfer that way.

There is also a circular select brush with xray on in top view after you have hidden bits you dont want you can select a circular selection (I hope you get what Im thinking of here…)

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OK thanks a lot for your time.
I need to select all that is below the top surface, so also those side walls, etc.
But think it’s going to be super complicated using Blender.
I was really hoping there’d be a way to use another object to select all the faces that are “inside” it.
I think I’m going to try and cheat by creating a second object to cover the surface of the first one.
Thanks anyway

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