Found on: any camera that came with triangular or round split rings; most Fujifilm; pro-level Nikon; Leica; Olympus; Sony; most vintage 35mm cameras; Also known as a “round” or “ring” mount.
Flat Mount
Found on: most Canon; entry- and mid-level Nikon; Fujifilm GFX 50S (connect strap to Fuji-supplied attachment clips), X-T100, X-A Series; vintage Rolleiflex. Also known as a “slotted” or “rectangular” mount.