Okay, I can't stand it any longer! I am going to take a cue from Dr. Benz, and start arguing semantics.
When I was young (a few years ago), cars usually had something that covered up a part of their wheel. If this thing covered only the center (hub) of the wheel, and left the rest of the wheel visible, it was called a "hub cap" (for obvious reasons). If this thing covered not only the hub of the wheel, but the entire thing, it was called a "wheel cover". Might not this terminology be easier than the confusing use of both hub cap and wheel cover to refer to either, followed by some description like 1-piece or 2-piece, small or large, old or new, etc.?
I believe that early 113s came with hub caps and trim rings, and late 113s came with wheel covers. 'Sorry, I just had to say it.
-David Pease
'66 French 230SL