Took me a fair bit of fiddling, but I think I have it figured out. The tab goes through the hole from behind. Pull the whole collar as tight as possible then bend the tab back to lock it in place. Which set of holes to use depends on the shape of the bottleneck. It's a lots easier to use pliers to fit the stopper.
I've fitted them to a US 66cl bomber and a couple of Irish pint bottles which I've just filled with some cider. They're watertight so far and the next challenge will be to see how they hold up to the pressure.
