Hmmm. A set on pliers is usually enough when they are closed like in your picture. I've also used a big flat blade screwdriver to open them up further. Put the flat blade between the 2 loops and twist it open. You should end up with loops sitting on each side of the flat blade. It's a little tricky to get them onto a hose like that, but once on a hose, it's easy to slide them up the hose using that method.
They only have a narrow clamp range, so make sure you are not using a clamp that is too small for the hose.
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