How to tell between 1/2 and 3/4 ton hub caps?

[John Fabris]

Hi Gang,

I have done a search but it is still not clear to me how to identify these style caps between the 1/2 or 3/4 style? Anyone have some pointers?
Borrowed this pic from leddzep for sale posting.

So, domed in and yellow are 73 and later, domed out and blue are earlier. What about size difference? is it width or depth that determines 1/2 or 3/4?