Sizes Of Scott 2 Post International Albums???

Hi,
I've got a few of the Scott blue international two post albums. Part one is about 3 1/2 in thick, Part two comes in 3 1/2 and under 3 inches (thinner paper), and Part three comes in the smaller size.

OK, I just realized that there are larger blue 2 post albums out there, advertised at 4 1/2 inches. Is this correct, that there are really three thicknesses out there?

Oh, the "4 1/2" do not indicate "part 1 or whatever).

I think most of what you see for sale today are Regular and Jumbo which I think of as being 3" and 4" but I don't know what the nominal measurements really are. Some dealers advertise these as holding 300 and 400 pages, respectively. I use the Jumbos for my Part I collection but believe they may not hold up as well as the regular binders.