How do you correctly abbreviate that something is in "three dimensions" in formal writing? As per the title, would you write either "3D", "3d", or "3-d"?
I want to write something like:
The figure contains a 2D widget (left) and a 3D gadget (right).
Additionally, if I use the full phrase in a sentence, I gather that I write
The three-dimensional gadget is composed of independent two-dimensional widgets.
i.e. using a hyphen and the word "three". Would it also be allowed to write "3-dimensional"? Especially in a context where I want to contrast it with something else "2-dimensional" in the same (or adjacent) sentence, as the numerals stick out more?