Even if you have the terminology there is always an issue of communicating specific changes you want. You can always try going to the knowledge center on here and ready all the articles and info that is posted. My GF was driving me up a wall because she had an idea but had no way of really articulating it, she spend some time reading and was able to express it better. Also here are maybe a few ways you can try communicating your ideas.
Trying making reference points and using good ol' geometry terms i.e. I want the part of the ring/shank that is 180 degrees or directly below the center stone thinner.
Also, something that he might be able to do is send you a labeled version of the cad model. So it would actually have the specific measurements tagged to a specific point on the ring. This might be an easier approach, so you can say the bottom of the shank says "it is 3mm I want to know if we can make that 2.5mm".
The last idea you would need a scanner or fax machine, print out the cad designs and draw your desired changes. You can use arrows to point to specific areas or things you want done.
Lastly, try being open and telling them you do not know how to communicate the changes you want. These people do this for a living and more than likely have a profitable company, so I am willing to bet it is not the first time they have had to deal with this.
Good Luck!
