Joe, the hood came with both clamp-on and screw-in Series VI adapters. I've seen them both ways. My preference is the screw-in, so that one can use the reverse cap on the end of the stowed hood. Even if you don't have the screw-on reverse cap, you can at least put the 36mm lens cap over the screw-in adapter, which doesn't fly with the clamp-on one.
I expect that the clamp on ones are probably from the Canon V, VI, P and 7 era, with the later rounded cases with no finder storage. That's when all the hoods were black.
I don't think anyone would use the even earlier slip-on adapter, since it would maul the black paint on the front rim. I don't even use those on my chromed lenses.
I also use a clamp-on adapter for my rectangular hood for the 35 & 50, even though that's anachronistically modern, it came with a slip-on.