Umm...Bwibwi, I think you may be thinking of another type of hook. Circle hooks are indeed 3/4 circle, there is no such string contraption that I know of. Circle hooks can be great for bottom fishing halibut and bottom fish. The way they work is that the point is protected, so the fish really swallows the hook BUT, since the point is protected, it doesn't penetrate the fish's gut. when the fish moves away with the bait (and the hook too), the whole thing slides to the mouth of the fish and "curls" around the lip of the fish, this curl is accomplished by the shape of the hook, only then does it actually penetrate the fish's mouth, hence a "perfect hookset." The biggest problem people seem to have with these hooks is that you don't actually set the hook, it may be a little difficult to comprehend, but setting the hook pulls the hook right out without the point hitting anything.
Hope that clears things up a bit...
The other thing that I like about these hooks is tha fact that they really don't even need a barb, the shape of the hook, and location of the point has all the holding power a person would really need.
If it's barbless, and the fish is out of the water, unhooking it shouldn't be too difficult, with a barb, and it's a whole new game, you literally have to tear a part of the fish's face off, but when hali fihsing, you kill most of what you catch anyway.
Now that we have that out of the way, back to the original question...