The "Waist Level Viewer 2" is an older item that predates cameras with the larger viewfinder eyepiece like the 5D III and 7D II. (itdoes not include an adapter for the larger square eyepiece adapter for the 5D III, 7D, 7D II, etc.)
It usually includes the "Adapter RM" which fits most camers with a small square eyepiece. If you have a Canon F-1 with a round eyepice, it would screw in directly without the Adapter.
Older Canon Angle Finders from the 60's used mirrors and had a reversed image. ("Waist Level Viewer", "Waist Level Viewer 2", "Angle Finder A", and "Angle Finder A2") The Angle Finder A2 and Angle Finder B should come with the "Adapter S" which also fits the small squre eyepices.
The "Angle Finder B" and Angle Finder C" use prisms and have a corrected image. The Angle Finder C includes both the EC-C and ED-C adapters (ED-C fits the large square eyepieces of the 5D III and 7D II).
