How would you make this?

[micheus]

I think that 18WU and 5WU could be the same as 18mm and 5mm when imported in another software or exported in stl... right?

For STL maybe in accordance with a post made by one user which tested in his 3D printer. For other formats, I think only DAE has a more specific option for that (as in that post was said).


So, about the how to make this ring question...

There are many ways to build it, for sure. Someone can use a different approach of modeling from the one I used or can do most the task using boolean tool (in this case, usually we have extra work adjusting the mesh).
I'm going to show some steps to get the basic shape for this ring. The refinement I will skip - to much work.


I started preparing the references using the images you linked and load them with Image Plane (front and top).

At the end the reference seems to not be so accurate, since when I scaled the ring to have the 18mm in the inner circumference the diamond diameter was greater than the 5mm you said. So, the steps are more a guide, but without precision.

I stated by creating the very basic ring shape using a Tube primitive:



I started my approach using Virtual Mirror over half of the tube, but I ended by realising that was not relevant in this step. So, once you understand the sequence of commands you can ignore this part when I created a virtual mirror:



The start point here is using the virtual mirror to replicate the other half of the object. But, you need only to work in half it if because we are going to replicate these work for all the "four quadrant" of the object (left-right and back-front):


Here is when we replicate the area we worked to the other quadrants:



These next two images will show how to build the base shape of this ring:






Here is the final result. No much polishment or other missing details, but it looks similar to the one in the image you shared.
What I took care was about the mesh arrangement. As you can see, the Work Mode shows the model almost as smooth as after apply Smooth Preview (which will make one subdivision):