On a diamond rated "thin - medium" 3.5% girdle, does this mean some parts are thin and some medium? do i need to be concerned in certain settings that it may chip, or is it fine since it is just not rated thin?
When you have a diamond with a very thin in its description, you have much more to worry about. You also want to stay away from very thick, since that can hide a LOT of weight. It may even enable a cutter to cut a stone of 1.00 or 1.01 that should properly weight less than a carat.
This is true of other price jump weights, like 1.5 and 2 ct. Hide enough weight in the girdle and your diamond suddenly sells for more, even though it is worth far less in actual value if beauty and sparkle are in your desired attributes for your diamond.